diff --git a/markitect/cli.py b/markitect/cli.py
index a66d4cdb..99c719e0 100644
--- a/markitect/cli.py
+++ b/markitect/cli.py
@@ -29,6 +29,7 @@ from .database import DatabaseManager
 from .legacy_compat import LegacyMode, emit_deprecation_warning, legacy_switch_option
 from .__version__ import get_version_info, get_release_info
 from .batch_processor import BatchProcessor, ProcessingMode, ErrorHandling, create_file_processor
+from .config_manager import ConfigurationManager
 
 # Import legacy system components for advanced management
 try:
@@ -4744,6 +4745,301 @@ def recursive(config, directory, depth, operation, pattern, error_handling, quie
         sys.exit(1)
 
 
+# Configuration Management Commands - Issue #18
+
+
+@cli.command(name='config-show')
+@click.option('--format', 'output_format', type=click.Choice(['yaml', 'json', 'simple']),
+              default='yaml', help='Output format for configuration display')
+@click.option('--show-sensitive', is_flag=True, help='Show sensitive values (tokens, passwords)')
+@pass_config
+def config_show(config, output_format, show_sensitive):
+    """Display current configuration.
+
+    Shows comprehensive configuration information including current settings,
+    file sources, environment variables, and workspace information.
+
+    Examples:
+        markitect config-show
+        markitect config-show --format json
+        markitect config-show --format simple --show-sensitive
+    """
+    try:
+        config_manager = ConfigurationManager()
+        output = config_manager.display_config(
+            show_sensitive=show_sensitive,
+            output_format=output_format
+        )
+        click.echo(output)
+
+    except Exception as e:
+        click.echo(f"Failed to display configuration: {e}", err=True)
+        if config.get('verbose'):
+            import traceback
+            click.echo(traceback.format_exc(), err=True)
+        sys.exit(1)
+
+
+@cli.command(name='config-set')
+@click.argument('key', type=str)
+@click.argument('value', type=str)
+@click.option('--config-file', type=click.Path(), help='Target configuration file')
+@click.option('--validate/--no-validate', default=True, help='Validate configuration after setting')
+@pass_config
+def config_set(config, key, value, config_file, validate):
+    """Set configuration values.
+
+    Sets a configuration value and persists it to a configuration file.
+    Supports nested keys using dot notation (e.g., 'gitea.url').
+
+    Examples:
+        markitect config-set gitea_url http://localhost:3000
+        markitect config-set repo_owner myorganization
+        markitect config-set api_token abc123def456
+        markitect config-set workspace.dir ./my_workspace
+    """
+    try:
+        config_manager = ConfigurationManager()
+
+        # Set the configuration value
+        success = config_manager.set_config_value(key, value, config_file)
+
+        if success:
+            click.echo(f"✅ Configuration updated: {key} = {value}")
+
+            # Show which file was updated
+            target_file = config_manager._get_target_config_file(config_file)
+            click.echo(f"📁 Updated file: {target_file}")
+
+            # Validate configuration if requested
+            if validate:
+                validation_results = config_manager.validate_configuration()
+                errors = [r for r in validation_results if r['status'] == 'error']
+                if errors:
+                    click.echo("⚠️  Configuration validation warnings:")
+                    for error in errors:
+                        click.echo(f"   • {error['key']}: {error['message']}")
+
+        else:
+            click.echo(f"❌ Failed to set configuration: {key}", err=True)
+            sys.exit(1)
+
+    except ValueError as e:
+        click.echo(f"❌ Configuration error: {e}", err=True)
+        sys.exit(1)
+    except Exception as e:
+        click.echo(f"❌ Failed to set configuration: {e}", err=True)
+        if config.get('verbose'):
+            import traceback
+            click.echo(traceback.format_exc(), err=True)
+        sys.exit(1)
+
+
+@cli.command(name='config-init')
+@click.option('--project-dir', type=click.Path(path_type=Path), help='Target project directory')
+@click.option('--interactive/--no-interactive', default=True, help='Interactive configuration setup')
+@click.option('--force', is_flag=True, help='Overwrite existing configuration')
+@pass_config
+def config_init(config, project_dir, interactive, force):
+    """Initialize configuration for new project.
+
+    Creates a new configuration file with sensible defaults and sets up
+    the necessary directory structure for a MarkiTect project.
+
+    Examples:
+        markitect config-init
+        markitect config-init --project-dir ./my-project
+        markitect config-init --no-interactive --force
+    """
+    try:
+        target_dir = project_dir or Path.cwd()
+        config_file = target_dir / '.markitect.yml'
+
+        # Check if configuration already exists
+        if config_file.exists() and not force:
+            click.echo(f"❌ Configuration file already exists: {config_file}")
+            click.echo("   Use --force to overwrite or choose a different directory")
+            sys.exit(1)
+
+        config_manager = ConfigurationManager()
+
+        # Interactive setup if requested
+        initial_config = {
+            'gitea_url': 'http://localhost:3000',
+            'repo_owner': '',
+            'repo_name': target_dir.name,
+            'workspace_dir': '.markitect_workspace',
+            'cache_dir': '.ast_cache',
+            'tests_dir': 'tests',
+            'test_file_pattern': 'test_issue_{issue_num}_{scenario}.py',
+            'claude_code_command': 'claude'
+        }
+
+        if interactive:
+            click.echo("🔧 Interactive MarkiTect configuration setup")
+            click.echo(f"📁 Target directory: {target_dir}")
+            click.echo()
+
+            # Prompt for each configuration value
+            initial_config['gitea_url'] = click.prompt(
+                'Gitea server URL',
+                default=initial_config['gitea_url']
+            )
+            initial_config['repo_owner'] = click.prompt(
+                'Repository owner/organization',
+                default=initial_config['repo_owner']
+            )
+            initial_config['repo_name'] = click.prompt(
+                'Repository name',
+                default=initial_config['repo_name']
+            )
+
+            if click.confirm('Configure API token now?', default=False):
+                initial_config['api_token'] = click.prompt(
+                    'API token',
+                    default='',
+                    hide_input=True
+                )
+
+            initial_config['workspace_dir'] = click.prompt(
+                'Workspace directory',
+                default=initial_config['workspace_dir']
+            )
+            initial_config['tests_dir'] = click.prompt(
+                'Tests directory',
+                default=initial_config['tests_dir']
+            )
+
+        # Initialize the project
+        result = config_manager.initialize_project_config(target_dir, interactive=False)
+
+        # Update with interactive values if provided
+        if interactive:
+            config_manager._save_config_file(initial_config, config_file)
+            result['config'] = initial_config
+
+        click.echo("✅ MarkiTect project initialized successfully!")
+        click.echo(f"📄 Configuration file: {result['config_file']}")
+        click.echo("📁 Created directories:")
+        for directory in result['created_directories']:
+            click.echo(f"   • {directory}")
+
+        # Show validation results
+        validation_results = config_manager.validate_configuration(result['config'])
+        warnings = [r for r in validation_results if r['status'] == 'warning']
+        errors = [r for r in validation_results if r['status'] == 'error']
+
+        if warnings:
+            click.echo("⚠️  Configuration warnings:")
+            for warning in warnings:
+                click.echo(f"   • {warning['message']}")
+
+        if errors:
+            click.echo("❌ Configuration errors:")
+            for error in errors:
+                click.echo(f"   • {error['message']}")
+        else:
+            click.echo("🎉 Configuration validation passed!")
+
+    except Exception as e:
+        click.echo(f"❌ Failed to initialize configuration: {e}", err=True)
+        if config.get('verbose'):
+            import traceback
+            click.echo(traceback.format_exc(), err=True)
+        sys.exit(1)
+
+
+@cli.command(name='config-validate')
+@click.option('--verbose', '-v', is_flag=True, help='Show detailed validation information')
+@pass_config
+def config_validate(config, verbose):
+    """Validate current configuration.
+
+    Checks the current configuration for common issues, missing required fields,
+    and validates paths and URLs. Provides suggestions for fixing any problems.
+
+    Examples:
+        markitect config-validate
+        markitect config-validate --verbose
+    """
+    try:
+        config_manager = ConfigurationManager()
+        validation_results = config_manager.validate_configuration()
+
+        # Categorize results
+        errors = [r for r in validation_results if r['status'] == 'error']
+        warnings = [r for r in validation_results if r['status'] == 'warning']
+        ok_results = [r for r in validation_results if r['status'] == 'ok']
+
+        # Display summary
+        click.echo(f"📊 Configuration Validation Summary:")
+        click.echo(f"   ✅ OK: {len(ok_results)}")
+        click.echo(f"   ⚠️  Warnings: {len(warnings)}")
+        click.echo(f"   ❌ Errors: {len(errors)}")
+        click.echo()
+
+        # Show errors
+        if errors:
+            click.echo("❌ Configuration Errors:")
+            for error in errors:
+                click.echo(f"   • {error['key']}: {error['message']}")
+            click.echo()
+
+        # Show warnings
+        if warnings:
+            click.echo("⚠️  Configuration Warnings:")
+            for warning in warnings:
+                click.echo(f"   • {warning['key']}: {warning['message']}")
+            click.echo()
+
+        # Show OK results in verbose mode
+        if verbose and ok_results:
+            click.echo("✅ Valid Configuration:")
+            for ok_result in ok_results:
+                click.echo(f"   • {ok_result['key']}: {ok_result['message']}")
+            click.echo()
+
+        # Overall status
+        if errors:
+            click.echo("❌ Configuration validation failed")
+            sys.exit(1)
+        elif warnings:
+            click.echo("⚠️  Configuration validation passed with warnings")
+        else:
+            click.echo("✅ Configuration validation passed")
+
+    except Exception as e:
+        click.echo(f"❌ Configuration validation failed: {e}", err=True)
+        if config.get('verbose'):
+            import traceback
+            click.echo(traceback.format_exc(), err=True)
+        sys.exit(1)
+
+
+@cli.command(name='config-help')
+@click.argument('key', required=False)
+@pass_config
+def config_help(config, key):
+    """Get help information for configuration keys.
+
+    Provides detailed information about available configuration options,
+    their purposes, and example values.
+
+    Examples:
+        markitect config-help
+        markitect config-help gitea_url
+        markitect config-help api_token
+    """
+    try:
+        config_manager = ConfigurationManager()
+        help_text = config_manager.get_config_help(key)
+        click.echo(help_text)
+
+    except Exception as e:
+        click.echo(f"❌ Failed to get configuration help: {e}", err=True)
+        sys.exit(1)
+
+
 # Register issue management commands
 cli.add_command(issues_group)
 
diff --git a/markitect/config_manager.py b/markitect/config_manager.py
new file mode 100644
index 00000000..92763674
--- /dev/null
+++ b/markitect/config_manager.py
@@ -0,0 +1,490 @@
+"""
+Configuration and Environment Management - Issue #18
+
+This module provides comprehensive configuration management capabilities for MarkiTect,
+allowing users to manage configuration and environment settings through CLI commands.
+
+Features:
+- Display current configuration with optional sensitive data masking
+- Set configuration values with validation
+- Initialize configuration for new projects
+- Configuration validation and help
+- Integration with existing configuration system
+- Environment variable management
+- Project-specific configuration support
+
+Commands implemented:
+- config-show: Display current configuration
+- config-set: Set configuration values
+- config-init: Initialize configuration for new project
+"""
+
+import os
+import json
+import yaml
+from pathlib import Path
+from typing import Dict, Any, Optional, List, Union, Tuple
+from dataclasses import asdict, fields
+from copy import deepcopy
+
+import click
+
+
+class ConfigurationManager:
+    """Core configuration management functionality."""
+
+    def __init__(self):
+        self.config_file_names = [
+            '.markitect.yml',
+            '.markitect.yaml',
+            '.markitect.json',
+            'markitect.config.yml',
+            'markitect.config.yaml',
+            'markitect.config.json'
+        ]
+        self.sensitive_keys = {
+            'api_token', 'token', 'password', 'secret', 'key',
+            'gitea_token', 'github_token', 'auth_token'
+        }
+
+    def get_current_config(self) -> Dict[str, Any]:
+        """Get current configuration from all sources."""
+        config = {}
+
+        # Load from existing configuration system
+        try:
+            from config.manager import MarkitectConfig
+            markitect_config = MarkitectConfig()
+            config = asdict(markitect_config)
+
+            # Convert Path objects to strings for JSON serialization
+            for key, value in config.items():
+                if isinstance(value, Path):
+                    config[key] = str(value)
+
+        except (ImportError, Exception):
+            # Fallback to basic configuration
+            config = {
+                'gitea_url': os.getenv('MARKITECT_GITEA_URL', 'http://localhost:3000'),
+                'repo_owner': os.getenv('MARKITECT_REPO_OWNER', ''),
+                'repo_name': os.getenv('MARKITECT_REPO_NAME', ''),
+                'api_token': os.getenv('MARKITECT_API_TOKEN', ''),
+                'workspace_dir': os.getenv('MARKITECT_WORKSPACE_DIR', '.markitect_workspace'),
+                'database_path': os.getenv('MARKITECT_DATABASE_PATH', str(Path.home() / '.markitect' / 'markitect.db')),
+                'cache_dir': os.getenv('MARKITECT_CACHE_DIR', '.ast_cache'),
+                'tests_dir': os.getenv('MARKITECT_TESTS_DIR', 'tests'),
+                'test_file_pattern': os.getenv('MARKITECT_TEST_FILE_PATTERN', 'test_issue_{issue_num}_{scenario}.py'),
+                'claude_code_command': os.getenv('MARKITECT_CLAUDE_CODE_COMMAND', 'claude')
+            }
+
+        # Add metadata about configuration sources
+        config['_meta'] = {
+            'config_sources': self._get_config_sources(),
+            'env_variables': self._get_relevant_env_vars(),
+            'working_directory': str(Path.cwd()),
+            'config_file_locations': self._get_config_file_locations()
+        }
+
+        return config
+
+    def _get_config_sources(self) -> List[str]:
+        """Get list of configuration sources in order of precedence."""
+        sources = []
+
+        # Check for config files
+        for config_name in self.config_file_names:
+            if Path(config_name).exists():
+                sources.append(f"File: {config_name}")
+
+        # Check for environment variables
+        env_vars = [key for key in os.environ.keys() if key.startswith('MARKITECT_')]
+        if env_vars:
+            sources.append(f"Environment variables: {len(env_vars)} found")
+
+        # Always include defaults
+        sources.append("Built-in defaults")
+
+        return sources
+
+    def _get_relevant_env_vars(self) -> Dict[str, str]:
+        """Get MARKITECT-related environment variables."""
+        env_vars = {}
+        for key, value in os.environ.items():
+            if key.startswith('MARKITECT_'):
+                env_vars[key] = value
+        return env_vars
+
+    def _get_config_file_locations(self) -> Dict[str, bool]:
+        """Get status of potential config file locations."""
+        locations = {}
+
+        # Current directory
+        for config_name in self.config_file_names:
+            current_dir_path = Path.cwd() / config_name
+            locations[str(current_dir_path)] = current_dir_path.exists()
+
+        # Home directory
+        home_config = Path.home() / '.markitect' / 'config.yml'
+        locations[str(home_config)] = home_config.exists()
+
+        return locations
+
+    def display_config(self, show_sensitive: bool = False, output_format: str = 'yaml') -> str:
+        """Display current configuration in specified format."""
+        config = self.get_current_config()
+
+        if not show_sensitive:
+            config = self._mask_sensitive_data(config)
+
+        if output_format == 'json':
+            return json.dumps(config, indent=2, default=str)
+        elif output_format == 'yaml':
+            return yaml.dump(config, default_flow_style=False, sort_keys=True)
+        else:
+            # Simple format
+            return self._format_simple(config)
+
+    def _mask_sensitive_data(self, config: Dict[str, Any]) -> Dict[str, Any]:
+        """Mask sensitive configuration values."""
+        masked_config = deepcopy(config)
+
+        def mask_recursive(obj):
+            if isinstance(obj, dict):
+                for key, value in obj.items():
+                    if any(sensitive in key.lower() for sensitive in self.sensitive_keys):
+                        if value and str(value).strip():
+                            obj[key] = '***MASKED***'
+                    else:
+                        mask_recursive(value)
+            elif isinstance(obj, list):
+                for item in obj:
+                    mask_recursive(item)
+
+        mask_recursive(masked_config)
+        return masked_config
+
+    def _format_simple(self, config: Dict[str, Any]) -> str:
+        """Format configuration in simple key=value style."""
+        lines = []
+
+        def format_recursive(obj, prefix=''):
+            if isinstance(obj, dict):
+                for key, value in sorted(obj.items()):
+                    full_key = f"{prefix}{key}" if prefix else key
+                    if isinstance(value, (dict, list)):
+                        if key != '_meta':  # Skip meta in simple format
+                            format_recursive(value, f"{full_key}.")
+                    else:
+                        lines.append(f"{full_key} = {value}")
+            elif isinstance(obj, list):
+                for i, item in enumerate(obj):
+                    format_recursive(item, f"{prefix}{i}.")
+
+        format_recursive(config)
+        return '\n'.join(lines)
+
+    def set_config_value(self, key: str, value: str, config_file: Optional[str] = None) -> bool:
+        """Set a configuration value and persist it."""
+        # Determine target config file
+        target_file = self._get_target_config_file(config_file)
+
+        # Load existing config from file
+        existing_config = self._load_config_file(target_file) if target_file.exists() else {}
+
+        # Set the value (support nested keys with dot notation)
+        self._set_nested_value(existing_config, key, value)
+
+        # Validate the new configuration
+        validation_errors = self._validate_config_value(key, value)
+        if validation_errors:
+            raise ValueError(f"Configuration validation failed: {'; '.join(validation_errors)}")
+
+        # Save back to file
+        self._save_config_file(existing_config, target_file)
+
+        return True
+
+    def _get_target_config_file(self, config_file: Optional[str] = None) -> Path:
+        """Determine target configuration file."""
+        if config_file:
+            return Path(config_file)
+
+        # Look for existing config file
+        for config_name in self.config_file_names:
+            config_path = Path(config_name)
+            if config_path.exists():
+                return config_path
+
+        # Default to .markitect.yml in current directory
+        return Path('.markitect.yml')
+
+    def _load_config_file(self, config_file: Path) -> Dict[str, Any]:
+        """Load configuration from file."""
+        try:
+            content = config_file.read_text()
+
+            if config_file.suffix in ['.yml', '.yaml']:
+                return yaml.safe_load(content) or {}
+            elif config_file.suffix == '.json':
+                return json.loads(content)
+            else:
+                # Try YAML first, then JSON
+                try:
+                    return yaml.safe_load(content) or {}
+                except yaml.YAMLError:
+                    return json.loads(content)
+
+        except Exception as e:
+            raise ValueError(f"Failed to load config file {config_file}: {e}")
+
+    def _save_config_file(self, config: Dict[str, Any], config_file: Path) -> None:
+        """Save configuration to file."""
+        try:
+            # Ensure directory exists
+            config_file.parent.mkdir(parents=True, exist_ok=True)
+
+            if config_file.suffix in ['.yml', '.yaml']:
+                content = yaml.dump(config, default_flow_style=False, sort_keys=True)
+            elif config_file.suffix == '.json':
+                content = json.dumps(config, indent=2, sort_keys=True)
+            else:
+                # Default to YAML
+                content = yaml.dump(config, default_flow_style=False, sort_keys=True)
+
+            config_file.write_text(content)
+
+        except Exception as e:
+            raise ValueError(f"Failed to save config file {config_file}: {e}")
+
+    def _set_nested_value(self, config: Dict[str, Any], key: str, value: str) -> None:
+        """Set a nested configuration value using dot notation."""
+        keys = key.split('.')
+        current = config
+
+        # Navigate to the parent of the target key
+        for k in keys[:-1]:
+            if k not in current:
+                current[k] = {}
+            current = current[k]
+
+        # Set the final value
+        final_key = keys[-1]
+
+        # Try to convert value to appropriate type
+        converted_value = self._convert_value(value)
+        current[final_key] = converted_value
+
+    def _convert_value(self, value: str) -> Any:
+        """Convert string value to appropriate type."""
+        # Handle boolean values
+        if value.lower() in ('true', 'yes', 'on', '1'):
+            return True
+        elif value.lower() in ('false', 'no', 'off', '0'):
+            return False
+
+        # Try to convert to number
+        try:
+            if '.' in value:
+                return float(value)
+            else:
+                return int(value)
+        except ValueError:
+            pass
+
+        # Return as string
+        return value
+
+    def _validate_config_value(self, key: str, value: str) -> List[str]:
+        """Validate a configuration value."""
+        errors = []
+
+        # Path validation
+        if any(path_key in key.lower() for path_key in ['dir', 'path', 'file']):
+            if value and not self._is_valid_path(value):
+                errors.append(f"'{value}' is not a valid path format")
+
+        # URL validation
+        if 'url' in key.lower():
+            if value and not self._is_valid_url(value):
+                errors.append(f"'{value}' is not a valid URL format")
+
+        # Required field validation for setting values (not for display)
+        # We only enforce required fields when explicitly setting them
+        if key == 'gitea_url' and not value.strip():
+            errors.append(f"'{key}' is required and cannot be empty")
+        elif key == 'database_path' and not value.strip():
+            errors.append(f"'{key}' is required and cannot be empty")
+
+        return errors
+
+    def _is_valid_path(self, path_str: str) -> bool:
+        """Check if a string represents a valid path."""
+        try:
+            Path(path_str)
+            return True
+        except (ValueError, OSError):
+            return False
+
+    def _is_valid_url(self, url_str: str) -> bool:
+        """Check if a string represents a valid URL."""
+        import re
+        url_pattern = re.compile(
+            r'^https?://'  # http:// or https://
+            r'(?:(?:[A-Z0-9](?:[A-Z0-9-]{0,61}[A-Z0-9])?\.)+[A-Z]{2,6}\.?|'  # domain...
+            r'localhost|'  # localhost...
+            r'\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})'  # ...or ip
+            r'(?::\d+)?'  # optional port
+            r'(?:/?|[/?]\S+)$', re.IGNORECASE)
+        return url_pattern.match(url_str) is not None
+
+    def initialize_project_config(self, project_dir: Optional[Path] = None, interactive: bool = True) -> Dict[str, Any]:
+        """Initialize configuration for a new project."""
+        target_dir = project_dir or Path.cwd()
+        config_file = target_dir / '.markitect.yml'
+
+        # Default configuration template
+        default_config = {
+            'gitea_url': 'http://localhost:3000',
+            'repo_owner': '',
+            'repo_name': target_dir.name,
+            'workspace_dir': '.markitect_workspace',
+            'cache_dir': '.ast_cache',
+            'tests_dir': 'tests',
+            'test_file_pattern': 'test_issue_{issue_num}_{scenario}.py',
+            'claude_code_command': 'claude'
+        }
+
+        if interactive:
+            default_config = self._interactive_config_setup(default_config)
+
+        # Create necessary directories
+        workspace_dir = target_dir / default_config['workspace_dir']
+        cache_dir = target_dir / default_config['cache_dir']
+        tests_dir = target_dir / default_config['tests_dir']
+
+        for directory in [workspace_dir, cache_dir, tests_dir]:
+            directory.mkdir(parents=True, exist_ok=True)
+
+        # Save configuration
+        self._save_config_file(default_config, config_file)
+
+        return {
+            'config_file': str(config_file),
+            'config': default_config,
+            'created_directories': [str(workspace_dir), str(cache_dir), str(tests_dir)]
+        }
+
+    def _interactive_config_setup(self, config: Dict[str, Any]) -> Dict[str, Any]:
+        """Interactive configuration setup (would be used with CLI)."""
+        # This method would be called by CLI with click.prompt()
+        # For now, return the default config
+        # The CLI integration will handle the interactive prompts
+        return config
+
+    def list_config_keys(self) -> List[Tuple[str, str, Any]]:
+        """List all available configuration keys with descriptions."""
+        config_schema = [
+            ('gitea_url', 'Gitea server URL', 'http://localhost:3000'),
+            ('repo_owner', 'Repository owner/organization', ''),
+            ('repo_name', 'Repository name', ''),
+            ('api_token', 'API token for authentication', ''),
+            ('workspace_dir', 'Workspace directory path', '.markitect_workspace'),
+            ('database_path', 'Database file path', '~/.markitect/markitect.db'),
+            ('cache_dir', 'AST cache directory', '.ast_cache'),
+            ('tests_dir', 'Tests directory', 'tests'),
+            ('test_file_pattern', 'Test file naming pattern', 'test_issue_{issue_num}_{scenario}.py'),
+            ('claude_code_command', 'Claude Code command', 'claude'),
+        ]
+
+        return config_schema
+
+    def get_config_help(self, key: Optional[str] = None) -> str:
+        """Get help information for configuration."""
+        if key:
+            # Get help for specific key
+            for config_key, description, default in self.list_config_keys():
+                if config_key == key:
+                    return f"{config_key}: {description} (default: {default})"
+            return f"Unknown configuration key: {key}"
+        else:
+            # Get general help
+            lines = ["Available configuration keys:"]
+            for config_key, description, default in self.list_config_keys():
+                lines.append(f"  {config_key:<20} {description}")
+            return '\n'.join(lines)
+
+    def validate_configuration(self, config: Optional[Dict[str, Any]] = None) -> List[Dict[str, Any]]:
+        """Validate current or provided configuration."""
+        if config is None:
+            config = self.get_current_config()
+
+        validation_results = []
+
+        # Check required fields
+        required_fields = ['gitea_url', 'database_path']
+        for field in required_fields:
+            if field not in config or not config[field]:
+                validation_results.append({
+                    'key': field,
+                    'status': 'error',
+                    'message': f'Required field {field} is missing or empty'
+                })
+            else:
+                validation_results.append({
+                    'key': field,
+                    'status': 'ok',
+                    'message': f'{field} is configured'
+                })
+
+        # Check paths exist or are creatable
+        path_fields = ['workspace_dir', 'cache_dir', 'tests_dir']
+        for field in path_fields:
+            if field in config:
+                path = Path(config[field])
+                if path.exists():
+                    validation_results.append({
+                        'key': field,
+                        'status': 'ok',
+                        'message': f'{field} exists at {path}'
+                    })
+                else:
+                    try:
+                        path.mkdir(parents=True, exist_ok=True)
+                        validation_results.append({
+                            'key': field,
+                            'status': 'warning',
+                            'message': f'{field} created at {path}'
+                        })
+                    except OSError as e:
+                        validation_results.append({
+                            'key': field,
+                            'status': 'error',
+                            'message': f'{field} cannot be created: {e}'
+                        })
+
+        # Check database path parent directory
+        if 'database_path' in config:
+            db_path = Path(config['database_path'])
+            db_parent = db_path.parent
+            if not db_parent.exists():
+                try:
+                    db_parent.mkdir(parents=True, exist_ok=True)
+                    validation_results.append({
+                        'key': 'database_path',
+                        'status': 'warning',
+                        'message': f'Database directory created at {db_parent}'
+                    })
+                except OSError as e:
+                    validation_results.append({
+                        'key': 'database_path',
+                        'status': 'error',
+                        'message': f'Cannot create database directory: {e}'
+                    })
+            else:
+                validation_results.append({
+                    'key': 'database_path',
+                    'status': 'ok',
+                    'message': f'Database directory exists at {db_parent}'
+                })
+
+        return validation_results
\ No newline at end of file
diff --git a/tests/test_issue_18_config_management.py b/tests/test_issue_18_config_management.py
new file mode 100644
index 00000000..c5e57bce
--- /dev/null
+++ b/tests/test_issue_18_config_management.py
@@ -0,0 +1,897 @@
+"""
+Tests for Issue #18: Configuration and Environment Management CLI
+
+This test suite verifies the configuration management functionality including:
+- Configuration display and management
+- Project initialization functionality
+- Configuration validation
+- Integration with existing config system
+- Environment variable handling
+"""
+
+import pytest
+import tempfile
+import shutil
+import os
+import json
+import yaml
+from pathlib import Path
+from unittest.mock import Mock, patch, MagicMock
+from click.testing import CliRunner
+
+from markitect.config_manager import ConfigurationManager
+from markitect.cli import cli
+
+
+class TestConfigurationManager:
+    """Test the core ConfigurationManager functionality."""
+
+    def setup_method(self):
+        """Set up test environment."""
+        self.temp_dir = tempfile.mkdtemp()
+        self.test_dir = Path(self.temp_dir)
+        self.original_cwd = os.getcwd()
+        os.chdir(self.temp_dir)
+
+    def teardown_method(self):
+        """Clean up test environment."""
+        os.chdir(self.original_cwd)
+        shutil.rmtree(self.temp_dir)
+
+    def test_get_current_config(self):
+        """Test getting current configuration."""
+        config_manager = ConfigurationManager()
+        config = config_manager.get_current_config()
+
+        # Should have basic configuration keys
+        expected_keys = [
+            'gitea_url', 'repo_owner', 'repo_name', 'api_token',
+            'workspace_dir', 'database_path', 'cache_dir', 'tests_dir'
+        ]
+
+        for key in expected_keys:
+            assert key in config
+
+        # Should have metadata
+        assert '_meta' in config
+        assert 'config_sources' in config['_meta']
+        assert 'env_variables' in config['_meta']
+        assert 'working_directory' in config['_meta']
+
+    def test_display_config_yaml_format(self):
+        """Test configuration display in YAML format."""
+        config_manager = ConfigurationManager()
+        output = config_manager.display_config(output_format='yaml')
+
+        # Should be valid YAML
+        parsed = yaml.safe_load(output)
+        assert isinstance(parsed, dict)
+        assert 'gitea_url' in parsed
+
+    def test_display_config_json_format(self):
+        """Test configuration display in JSON format."""
+        config_manager = ConfigurationManager()
+        output = config_manager.display_config(output_format='json')
+
+        # Should be valid JSON
+        parsed = json.loads(output)
+        assert isinstance(parsed, dict)
+        assert 'gitea_url' in parsed
+
+    def test_display_config_simple_format(self):
+        """Test configuration display in simple format."""
+        config_manager = ConfigurationManager()
+        output = config_manager.display_config(output_format='simple')
+
+        # Should contain key=value pairs
+        lines = output.split('\n')
+        assert any('gitea_url =' in line for line in lines)
+        assert any('repo_owner =' in line for line in lines)
+
+    def test_mask_sensitive_data(self):
+        """Test masking of sensitive configuration data."""
+        config_manager = ConfigurationManager()
+
+        # Create config with sensitive data
+        config = {
+            'api_token': 'secret123',
+            'password': 'mypassword',
+            'gitea_url': 'http://localhost:3000',
+            'repo_name': 'test-repo'
+        }
+
+        masked = config_manager._mask_sensitive_data(config)
+
+        # Sensitive fields should be masked
+        assert masked['api_token'] == '***MASKED***'
+        assert masked['password'] == '***MASKED***'
+
+        # Non-sensitive fields should remain
+        assert masked['gitea_url'] == 'http://localhost:3000'
+        assert masked['repo_name'] == 'test-repo'
+
+    def test_mask_sensitive_data_preserves_empty_values(self):
+        """Test that empty sensitive values are not masked."""
+        config_manager = ConfigurationManager()
+
+        config = {
+            'api_token': '',
+            'secret': None,
+            'repo_name': 'test-repo'
+        }
+
+        masked = config_manager._mask_sensitive_data(config)
+
+        # Empty/None values should not be masked
+        assert masked['api_token'] == ''
+        assert masked['secret'] is None
+        assert masked['repo_name'] == 'test-repo'
+
+    def test_set_config_value_simple(self):
+        """Test setting a simple configuration value."""
+        config_manager = ConfigurationManager()
+
+        success = config_manager.set_config_value('repo_name', 'test-repository')
+        assert success
+
+        # Verify file was created
+        config_file = self.test_dir / '.markitect.yml'
+        assert config_file.exists()
+
+        # Verify content
+        content = yaml.safe_load(config_file.read_text())
+        assert content['repo_name'] == 'test-repository'
+
+    def test_set_config_value_nested(self):
+        """Test setting nested configuration value with dot notation."""
+        config_manager = ConfigurationManager()
+
+        success = config_manager.set_config_value('gitea.url', 'http://example.com')
+        assert success
+
+        # Verify nested structure
+        config_file = self.test_dir / '.markitect.yml'
+        content = yaml.safe_load(config_file.read_text())
+        assert content['gitea']['url'] == 'http://example.com'
+
+    def test_set_config_value_type_conversion(self):
+        """Test automatic type conversion for configuration values."""
+        config_manager = ConfigurationManager()
+
+        # Test boolean conversion
+        config_manager.set_config_value('debug', 'true')
+        config_manager.set_config_value('verbose', 'false')
+
+        # Test number conversion
+        config_manager.set_config_value('port', '3000')
+        config_manager.set_config_value('timeout', '30.5')
+
+        config_file = self.test_dir / '.markitect.yml'
+        content = yaml.safe_load(config_file.read_text())
+
+        assert content['debug'] is True
+        assert content['verbose'] is False
+        assert content['port'] == 3000
+        assert content['timeout'] == 30.5
+
+    def test_set_config_value_validation_error(self):
+        """Test configuration validation during value setting."""
+        config_manager = ConfigurationManager()
+
+        # Test invalid URL
+        with pytest.raises(ValueError, match="not a valid URL format"):
+            config_manager.set_config_value('gitea_url', 'invalid-url')
+
+    def test_set_config_value_existing_file(self):
+        """Test setting values in existing configuration file."""
+        # Create existing config file
+        existing_config = {
+            'repo_name': 'old-name',
+            'gitea_url': 'http://localhost:3000'
+        }
+        config_file = self.test_dir / '.markitect.yml'
+        config_file.write_text(yaml.dump(existing_config))
+
+        config_manager = ConfigurationManager()
+        success = config_manager.set_config_value('repo_name', 'new-name')
+        assert success
+
+        # Verify update
+        content = yaml.safe_load(config_file.read_text())
+        assert content['repo_name'] == 'new-name'
+        assert content['gitea_url'] == 'http://localhost:3000'  # Should be preserved
+
+    def test_set_config_value_custom_file(self):
+        """Test setting values in custom configuration file."""
+        custom_file = self.test_dir / 'custom.yml'
+
+        config_manager = ConfigurationManager()
+        success = config_manager.set_config_value('repo_name', 'test', str(custom_file))
+        assert success
+
+        assert custom_file.exists()
+        content = yaml.safe_load(custom_file.read_text())
+        assert content['repo_name'] == 'test'
+
+    def test_initialize_project_config(self):
+        """Test project configuration initialization."""
+        config_manager = ConfigurationManager()
+        result = config_manager.initialize_project_config(self.test_dir, interactive=False)
+
+        # Verify config file created
+        config_file = Path(result['config_file'])
+        assert config_file.exists()
+        assert config_file.name == '.markitect.yml'
+
+        # Verify directories created
+        assert len(result['created_directories']) > 0
+        for directory in result['created_directories']:
+            assert Path(directory).exists()
+
+        # Verify config structure
+        config = result['config']
+        assert 'gitea_url' in config
+        assert 'repo_name' in config
+        assert config['repo_name'] == self.test_dir.name
+
+    def test_initialize_project_config_custom_dir(self):
+        """Test project initialization in custom directory."""
+        project_dir = self.test_dir / 'my-project'
+
+        config_manager = ConfigurationManager()
+        result = config_manager.initialize_project_config(project_dir, interactive=False)
+
+        # Verify correct location
+        config_file = Path(result['config_file'])
+        assert config_file.parent == project_dir
+        assert project_dir.exists()
+
+    def test_validate_configuration_success(self):
+        """Test configuration validation with valid config."""
+        config = {
+            'gitea_url': 'http://localhost:3000',
+            'database_path': str(self.test_dir / 'db.sqlite'),
+            'workspace_dir': str(self.test_dir / 'workspace'),
+            'cache_dir': str(self.test_dir / 'cache'),
+            'tests_dir': str(self.test_dir / 'tests')
+        }
+
+        config_manager = ConfigurationManager()
+        results = config_manager.validate_configuration(config)
+
+        # Should have validation results
+        assert len(results) > 0
+
+        # Check for required field validations
+        required_checks = [r for r in results if r['key'] in ['gitea_url', 'database_path']]
+        assert len(required_checks) > 0
+
+    def test_validate_configuration_missing_required(self):
+        """Test configuration validation with missing required fields."""
+        config = {
+            'repo_name': 'test'
+            # Missing gitea_url and database_path
+        }
+
+        config_manager = ConfigurationManager()
+        results = config_manager.validate_configuration(config)
+
+        # Should have errors for missing required fields
+        errors = [r for r in results if r['status'] == 'error']
+        assert len(errors) > 0
+
+        error_keys = [r['key'] for r in errors]
+        assert 'gitea_url' in error_keys or 'database_path' in error_keys
+
+    def test_validate_configuration_path_creation(self):
+        """Test configuration validation creates missing directories."""
+        config = {
+            'gitea_url': 'http://localhost:3000',
+            'database_path': str(self.test_dir / 'data' / 'db.sqlite'),
+            'workspace_dir': str(self.test_dir / 'new_workspace'),
+            'cache_dir': str(self.test_dir / 'new_cache'),
+            'tests_dir': str(self.test_dir / 'new_tests')
+        }
+
+        config_manager = ConfigurationManager()
+        results = config_manager.validate_configuration(config)
+
+        # Directories should be created
+        assert (self.test_dir / 'new_workspace').exists()
+        assert (self.test_dir / 'new_cache').exists()
+        assert (self.test_dir / 'new_tests').exists()
+        assert (self.test_dir / 'data').exists()  # Database parent directory
+
+        # Should have warnings for created directories
+        warnings = [r for r in results if r['status'] == 'warning']
+        assert len(warnings) > 0
+
+    def test_list_config_keys(self):
+        """Test listing available configuration keys."""
+        config_manager = ConfigurationManager()
+        keys = config_manager.list_config_keys()
+
+        # Should return list of tuples
+        assert isinstance(keys, list)
+        assert len(keys) > 0
+
+        # Each item should be (key, description, default)
+        for item in keys:
+            assert len(item) == 3
+            assert isinstance(item[0], str)  # key
+            assert isinstance(item[1], str)  # description
+
+        # Should include expected keys
+        key_names = [item[0] for item in keys]
+        assert 'gitea_url' in key_names
+        assert 'repo_name' in key_names
+        assert 'api_token' in key_names
+
+    def test_get_config_help_specific_key(self):
+        """Test getting help for specific configuration key."""
+        config_manager = ConfigurationManager()
+        help_text = config_manager.get_config_help('gitea_url')
+
+        assert 'gitea_url' in help_text
+        assert 'description' in help_text.lower() or ':' in help_text
+
+    def test_get_config_help_unknown_key(self):
+        """Test getting help for unknown configuration key."""
+        config_manager = ConfigurationManager()
+        help_text = config_manager.get_config_help('unknown_key')
+
+        assert 'unknown' in help_text.lower()
+
+    def test_get_config_help_general(self):
+        """Test getting general configuration help."""
+        config_manager = ConfigurationManager()
+        help_text = config_manager.get_config_help()
+
+        assert 'available' in help_text.lower() or 'configuration' in help_text.lower()
+        assert 'gitea_url' in help_text
+        assert 'repo_name' in help_text
+
+    def test_convert_value_booleans(self):
+        """Test value conversion for boolean types."""
+        config_manager = ConfigurationManager()
+
+        # True values
+        for true_val in ['true', 'True', 'TRUE', 'yes', 'YES', 'on', 'ON', '1']:
+            assert config_manager._convert_value(true_val) is True
+
+        # False values
+        for false_val in ['false', 'False', 'FALSE', 'no', 'NO', 'off', 'OFF', '0']:
+            assert config_manager._convert_value(false_val) is False
+
+    def test_convert_value_numbers(self):
+        """Test value conversion for numeric types."""
+        config_manager = ConfigurationManager()
+
+        # Integers
+        assert config_manager._convert_value('42') == 42
+        assert config_manager._convert_value('-10') == -10
+
+        # Floats
+        assert config_manager._convert_value('3.14') == 3.14
+        assert config_manager._convert_value('-2.5') == -2.5
+
+        # Strings that look like numbers but aren't
+        assert config_manager._convert_value('not-a-number') == 'not-a-number'
+
+    def test_is_valid_url(self):
+        """Test URL validation."""
+        config_manager = ConfigurationManager()
+
+        # Valid URLs
+        valid_urls = [
+            'http://localhost:3000',
+            'https://example.com',
+            'http://192.168.1.1:8080',
+            'https://api.github.com/repos'
+        ]
+        for url in valid_urls:
+            assert config_manager._is_valid_url(url), f"Should be valid: {url}"
+
+        # Invalid URLs
+        invalid_urls = [
+            'not-a-url',
+            'ftp://example.com',
+            'localhost:3000',
+            'http://',
+            ''
+        ]
+        for url in invalid_urls:
+            assert not config_manager._is_valid_url(url), f"Should be invalid: {url}"
+
+    def test_is_valid_path(self):
+        """Test path validation."""
+        config_manager = ConfigurationManager()
+
+        # Valid paths
+        valid_paths = [
+            '/absolute/path',
+            './relative/path',
+            '~/home/path',
+            'simple-path',
+            str(self.test_dir / 'subdir')
+        ]
+        for path in valid_paths:
+            assert config_manager._is_valid_path(path), f"Should be valid: {path}"
+
+        # Edge case: empty string (should be considered valid as it can represent current directory)
+        assert config_manager._is_valid_path('')
+
+
+class TestConfigFileParsing:
+    """Test configuration file parsing and saving."""
+
+    def setup_method(self):
+        """Set up test environment."""
+        self.temp_dir = tempfile.mkdtemp()
+        self.test_dir = Path(self.temp_dir)
+        self.original_cwd = os.getcwd()
+        os.chdir(self.temp_dir)
+
+    def teardown_method(self):
+        """Clean up test environment."""
+        os.chdir(self.original_cwd)
+        shutil.rmtree(self.temp_dir)
+
+    def test_load_yaml_config_file(self):
+        """Test loading YAML configuration file."""
+        config_content = {
+            'gitea_url': 'http://localhost:3000',
+            'repo_name': 'test-repo',
+            'nested': {
+                'key': 'value'
+            }
+        }
+
+        config_file = self.test_dir / 'test.yml'
+        config_file.write_text(yaml.dump(config_content))
+
+        config_manager = ConfigurationManager()
+        loaded = config_manager._load_config_file(config_file)
+
+        assert loaded == config_content
+
+    def test_load_json_config_file(self):
+        """Test loading JSON configuration file."""
+        config_content = {
+            'gitea_url': 'http://localhost:3000',
+            'repo_name': 'test-repo',
+            'debug': True
+        }
+
+        config_file = self.test_dir / 'test.json'
+        config_file.write_text(json.dumps(config_content))
+
+        config_manager = ConfigurationManager()
+        loaded = config_manager._load_config_file(config_file)
+
+        assert loaded == config_content
+
+    def test_save_yaml_config_file(self):
+        """Test saving YAML configuration file."""
+        config_content = {
+            'gitea_url': 'http://localhost:3000',
+            'repo_name': 'test-repo'
+        }
+
+        config_file = self.test_dir / 'output.yml'
+        config_manager = ConfigurationManager()
+        config_manager._save_config_file(config_content, config_file)
+
+        assert config_file.exists()
+        loaded = yaml.safe_load(config_file.read_text())
+        assert loaded == config_content
+
+    def test_save_json_config_file(self):
+        """Test saving JSON configuration file."""
+        config_content = {
+            'gitea_url': 'http://localhost:3000',
+            'repo_name': 'test-repo'
+        }
+
+        config_file = self.test_dir / 'output.json'
+        config_manager = ConfigurationManager()
+        config_manager._save_config_file(config_content, config_file)
+
+        assert config_file.exists()
+        loaded = json.loads(config_file.read_text())
+        assert loaded == config_content
+
+    def test_load_invalid_config_file(self):
+        """Test loading invalid configuration file."""
+        config_file = self.test_dir / 'invalid.yml'
+        config_file.write_text('invalid: yaml: content: [')
+
+        config_manager = ConfigurationManager()
+        with pytest.raises(ValueError, match="Failed to load config file"):
+            config_manager._load_config_file(config_file)
+
+    def test_get_target_config_file_existing(self):
+        """Test getting target config file when one exists."""
+        # Create an existing config file
+        existing_file = self.test_dir / '.markitect.yml'
+        existing_file.write_text('test: value')
+
+        config_manager = ConfigurationManager()
+        target = config_manager._get_target_config_file()
+
+        # Should be relative path that matches the existing file
+        assert target.name == existing_file.name
+        assert target.exists()
+
+    def test_get_target_config_file_default(self):
+        """Test getting target config file when none exists."""
+        config_manager = ConfigurationManager()
+        target = config_manager._get_target_config_file()
+
+        # Should be the default config file name
+        assert target.name == '.markitect.yml'
+
+    def test_get_target_config_file_custom(self):
+        """Test getting custom target config file."""
+        custom_file = 'custom-config.yml'
+
+        config_manager = ConfigurationManager()
+        target = config_manager._get_target_config_file(custom_file)
+
+        assert target == Path(custom_file)
+
+
+class TestCLIIntegration:
+    """Test CLI command integration."""
+
+    def setup_method(self):
+        """Set up test environment."""
+        self.temp_dir = tempfile.mkdtemp()
+        self.test_dir = Path(self.temp_dir)
+        self.original_cwd = os.getcwd()
+        os.chdir(self.temp_dir)
+        self.runner = CliRunner()
+
+    def teardown_method(self):
+        """Clean up test environment."""
+        os.chdir(self.original_cwd)
+        shutil.rmtree(self.temp_dir)
+
+    def test_config_show_command(self):
+        """Test config-show CLI command."""
+        result = self.runner.invoke(cli, ['config-show'])
+
+        assert result.exit_code == 0
+        assert 'gitea_url' in result.output
+
+    def test_config_show_command_json_format(self):
+        """Test config-show with JSON format."""
+        result = self.runner.invoke(cli, ['config-show', '--format', 'json'])
+
+        assert result.exit_code == 0
+        # Output should be valid JSON
+        try:
+            json.loads(result.output)
+        except json.JSONDecodeError:
+            pytest.fail("Output is not valid JSON")
+
+    def test_config_show_command_simple_format(self):
+        """Test config-show with simple format."""
+        result = self.runner.invoke(cli, ['config-show', '--format', 'simple'])
+
+        assert result.exit_code == 0
+        assert '=' in result.output  # Should contain key=value pairs
+
+    def test_config_set_command(self):
+        """Test config-set CLI command."""
+        result = self.runner.invoke(cli, [
+            'config-set', 'repo_name', 'test-repository'
+        ])
+
+        assert result.exit_code == 0
+        assert 'Configuration updated' in result.output
+
+        # Verify file was created
+        config_file = self.test_dir / '.markitect.yml'
+        assert config_file.exists()
+
+        content = yaml.safe_load(config_file.read_text())
+        assert content['repo_name'] == 'test-repository'
+
+    def test_config_set_command_nested_key(self):
+        """Test config-set with nested key."""
+        result = self.runner.invoke(cli, [
+            'config-set', 'gitea.url', 'http://example.com'
+        ])
+
+        assert result.exit_code == 0
+
+        config_file = self.test_dir / '.markitect.yml'
+        content = yaml.safe_load(config_file.read_text())
+        assert content['gitea']['url'] == 'http://example.com'
+
+    def test_config_set_command_custom_file(self):
+        """Test config-set with custom config file."""
+        custom_file = 'custom.yml'
+        result = self.runner.invoke(cli, [
+            'config-set', 'repo_name', 'test',
+            '--config-file', custom_file
+        ])
+
+        assert result.exit_code == 0
+        assert Path(custom_file).exists()
+
+    def test_config_set_command_no_validate(self):
+        """Test config-set with validation disabled."""
+        result = self.runner.invoke(cli, [
+            'config-set', 'repo_name', 'test',
+            '--no-validate'
+        ])
+
+        assert result.exit_code == 0
+
+    def test_config_set_command_validation_error(self):
+        """Test config-set with validation error."""
+        result = self.runner.invoke(cli, [
+            'config-set', 'gitea_url', 'invalid-url'
+        ])
+
+        assert result.exit_code == 1
+        assert 'Configuration error' in result.output
+
+    def test_config_init_command_non_interactive(self):
+        """Test config-init CLI command in non-interactive mode."""
+        result = self.runner.invoke(cli, [
+            'config-init', '--no-interactive'
+        ])
+
+        assert result.exit_code == 0
+        assert 'initialized successfully' in result.output
+
+        # Verify config file created
+        config_file = self.test_dir / '.markitect.yml'
+        assert config_file.exists()
+
+        # Verify directories created
+        assert (self.test_dir / '.markitect_workspace').exists()
+        assert (self.test_dir / '.ast_cache').exists()
+        assert (self.test_dir / 'tests').exists()
+
+    def test_config_init_command_custom_directory(self):
+        """Test config-init with custom project directory."""
+        project_dir = self.test_dir / 'my-project'
+
+        result = self.runner.invoke(cli, [
+            'config-init',
+            '--project-dir', str(project_dir),
+            '--no-interactive'
+        ])
+
+        assert result.exit_code == 0
+
+        # Verify in correct location
+        config_file = project_dir / '.markitect.yml'
+        assert config_file.exists()
+
+    def test_config_init_command_existing_file_no_force(self):
+        """Test config-init with existing file without force."""
+        # Create existing config file
+        config_file = self.test_dir / '.markitect.yml'
+        config_file.write_text('existing: config')
+
+        result = self.runner.invoke(cli, [
+            'config-init', '--no-interactive'
+        ])
+
+        assert result.exit_code == 1
+        assert 'already exists' in result.output
+
+    def test_config_init_command_existing_file_with_force(self):
+        """Test config-init with existing file with force."""
+        # Create existing config file
+        config_file = self.test_dir / '.markitect.yml'
+        config_file.write_text('existing: config')
+
+        result = self.runner.invoke(cli, [
+            'config-init', '--no-interactive', '--force'
+        ])
+
+        assert result.exit_code == 0
+        assert 'initialized successfully' in result.output
+
+    def test_config_validate_command(self):
+        """Test config-validate CLI command."""
+        result = self.runner.invoke(cli, ['config-validate'])
+
+        assert result.exit_code in [0, 1]  # May have warnings/errors
+        assert 'Configuration Validation Summary' in result.output
+
+    def test_config_validate_command_verbose(self):
+        """Test config-validate with verbose output."""
+        result = self.runner.invoke(cli, ['config-validate', '--verbose'])
+
+        assert result.exit_code in [0, 1]
+        assert 'Configuration Validation Summary' in result.output
+
+    def test_config_help_command_general(self):
+        """Test config-help CLI command."""
+        result = self.runner.invoke(cli, ['config-help'])
+
+        assert result.exit_code == 0
+        assert 'available' in result.output.lower() or 'configuration' in result.output.lower()
+        assert 'gitea_url' in result.output
+
+    def test_config_help_command_specific_key(self):
+        """Test config-help for specific key."""
+        result = self.runner.invoke(cli, ['config-help', 'gitea_url'])
+
+        assert result.exit_code == 0
+        assert 'gitea_url' in result.output
+
+    def test_config_help_command_unknown_key(self):
+        """Test config-help for unknown key."""
+        result = self.runner.invoke(cli, ['config-help', 'unknown_key'])
+
+        assert result.exit_code == 0
+        assert 'unknown' in result.output.lower()
+
+
+class TestEnvironmentVariables:
+    """Test environment variable handling."""
+
+    def setup_method(self):
+        """Set up test environment."""
+        self.temp_dir = tempfile.mkdtemp()
+        self.test_dir = Path(self.temp_dir)
+        self.original_cwd = os.getcwd()
+        os.chdir(self.temp_dir)
+
+        # Store original environment
+        self.original_env = dict(os.environ)
+
+    def teardown_method(self):
+        """Clean up test environment."""
+        os.chdir(self.original_cwd)
+        shutil.rmtree(self.temp_dir)
+
+        # Restore original environment
+        os.environ.clear()
+        os.environ.update(self.original_env)
+
+    def test_get_relevant_env_vars(self):
+        """Test getting MARKITECT-related environment variables."""
+        # Set some test environment variables
+        os.environ['MARKITECT_GITEA_URL'] = 'http://test.com'
+        os.environ['MARKITECT_REPO_NAME'] = 'test-repo'
+        os.environ['OTHER_VAR'] = 'should-be-ignored'
+
+        config_manager = ConfigurationManager()
+        env_vars = config_manager._get_relevant_env_vars()
+
+        assert 'MARKITECT_GITEA_URL' in env_vars
+        assert 'MARKITECT_REPO_NAME' in env_vars
+        assert 'OTHER_VAR' not in env_vars
+        assert env_vars['MARKITECT_GITEA_URL'] == 'http://test.com'
+
+    def test_config_with_env_vars(self):
+        """Test configuration loading with environment variables."""
+        # Set environment variables
+        os.environ['MARKITECT_GITEA_URL'] = 'http://env-test.com'
+        os.environ['MARKITECT_REPO_NAME'] = 'env-repo'
+
+        config_manager = ConfigurationManager()
+        config = config_manager.get_current_config()
+
+        # Environment variables should be reflected in config
+        assert config['gitea_url'] == 'http://env-test.com'
+        assert config['repo_name'] == 'env-repo'
+
+        # Should have env vars in metadata
+        assert 'MARKITECT_GITEA_URL' in config['_meta']['env_variables']
+        assert 'MARKITECT_REPO_NAME' in config['_meta']['env_variables']
+
+
+class TestEdgeCases:
+    """Test edge cases and error conditions."""
+
+    def setup_method(self):
+        """Set up test environment."""
+        self.temp_dir = tempfile.mkdtemp()
+        self.test_dir = Path(self.temp_dir)
+        self.original_cwd = os.getcwd()
+        os.chdir(self.temp_dir)
+
+    def teardown_method(self):
+        """Clean up test environment."""
+        os.chdir(self.original_cwd)
+        shutil.rmtree(self.temp_dir)
+
+    def test_config_manager_with_permission_error(self):
+        """Test handling permission errors."""
+        # Create a directory we can't write to
+        restricted_dir = self.test_dir / 'restricted'
+        restricted_dir.mkdir(mode=0o444)  # Read-only
+
+        config_manager = ConfigurationManager()
+
+        # This should not crash, but may warn about permission issues
+        try:
+            config = config_manager.get_current_config()
+            assert isinstance(config, dict)
+        except PermissionError:
+            # Acceptable to fail with permission error
+            pass
+
+    def test_set_config_value_invalid_file_path(self):
+        """Test setting config value with invalid file path."""
+        config_manager = ConfigurationManager()
+
+        # Try to write to a path that doesn't exist and can't be created
+        # Use a more reliable invalid path that doesn't depend on system permissions
+        invalid_path = '/nonexistent_directory_12345/config.yml'
+        with pytest.raises(ValueError):
+            config_manager.set_config_value('test', 'value', invalid_path)
+
+    def test_validate_configuration_with_none(self):
+        """Test configuration validation with None input."""
+        config_manager = ConfigurationManager()
+
+        # Should not crash with None input
+        results = config_manager.validate_configuration(None)
+        assert isinstance(results, list)
+
+    def test_mask_sensitive_data_with_complex_structure(self):
+        """Test masking sensitive data in complex nested structure."""
+        config_manager = ConfigurationManager()
+
+        complex_config = {
+            'database': {
+                'password': 'secret123',
+                'host': 'localhost'
+            },
+            'apis': [
+                {'name': 'github', 'token': 'ghp_secret'},
+                {'name': 'gitea', 'url': 'http://localhost:3000'}
+            ],
+            'secrets': {
+                'nested': {
+                    'api_key': 'very_secret'
+                }
+            }
+        }
+
+        masked = config_manager._mask_sensitive_data(complex_config)
+
+        # Sensitive fields should be masked at any level
+        assert masked['database']['password'] == '***MASKED***'
+        assert masked['apis'][0]['token'] == '***MASKED***'
+
+        # The 'secrets' key itself gets masked because it's a sensitive keyword
+        # This is actually correct behavior
+        assert masked['secrets'] == '***MASKED***'
+
+        # Non-sensitive fields should remain
+        assert masked['database']['host'] == 'localhost'
+        assert masked['apis'][1]['url'] == 'http://localhost:3000'
+
+    def test_get_config_sources_empty_directory(self):
+        """Test getting config sources in empty directory."""
+        config_manager = ConfigurationManager()
+        sources = config_manager._get_config_sources()
+
+        # Should always include defaults
+        assert len(sources) > 0
+        assert any('defaults' in source.lower() for source in sources)
+
+    def test_initialize_project_config_existing_directories(self):
+        """Test project initialization with existing directories."""
+        # Pre-create some directories
+        (self.test_dir / '.markitect_workspace').mkdir()
+        (self.test_dir / 'tests').mkdir()
+
+        config_manager = ConfigurationManager()
+        result = config_manager.initialize_project_config(self.test_dir, interactive=False)
+
+        # Should succeed even with existing directories
+        assert 'config_file' in result
+        assert Path(result['config_file']).exists()
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