diff --git a/Makefile b/Makefile
index ae9522c5..9669c13e 100644
--- a/Makefile
+++ b/Makefile
@@ -1,7 +1,7 @@
 # MarkiTect - Advanced Markdown Engine
 # Makefile for common development tasks
 
-.PHONY: help setup install test build clean update status dev lint format check-deps venv-status update-digest
+.PHONY: help setup install test build clean update status dev lint format check-deps venv-status update-digest add-diary-entry
 
 # Default target
 help:
@@ -30,7 +30,8 @@ help:
 	@echo "  check-deps  - Check dependency status"
 	@echo ""
 	@echo "Documentation:"
-	@echo "  update-digest - Update ProjectStatusDigest.md (requires Claude Code)"
+	@echo "  update-digest   - Update ProjectStatusDigest.md (requires Claude Code)"
+	@echo "  add-diary-entry - Add new entry to ProjectDiary.md (requires Claude Code)"
 
 # Python and virtual environment setup
 PYTHON := python3
@@ -174,3 +175,31 @@ update-digest:
 	@echo "   Command: 'Please update ProjectStatusDigest.md with the current project state'"
 	@echo ""
 	@echo "💡 Tip: You can also manually edit ProjectStatusDigest.md if needed"
+
+# Add new entry to project diary (requires Claude Code)
+add-diary-entry:
+	@echo "🔍 Checking for Claude Code availability..."
+	@if ! command -v claude >/dev/null 2>&1; then \
+		echo "❌ Claude Code not found in PATH"; \
+		echo "   This target requires Claude Code CLI to be installed"; \
+		echo "   Visit: https://claude.ai/code for installation instructions"; \
+		exit 1; \
+	fi
+	@echo "✅ Claude Code found"
+	@if [ ! -f ProjectDiary.md ]; then \
+		echo "❌ ProjectDiary.md not found"; \
+		echo "   Create the diary file first or run this from the project root"; \
+		exit 1; \
+	fi
+	@echo "📖 Adding new entry to ProjectDiary.md..."
+	@echo "   Please ask Claude Code to add a new diary entry for recent work"
+	@echo "   Command: 'Please add a new entry to ProjectDiary.md summarizing recent progress'"
+	@echo ""
+	@echo "📋 Entry should include:"
+	@echo "   - Date ($(shell date +%Y-%m-%d))"
+	@echo "   - One-line progress characterization"
+	@echo "   - Contributors since last entry"
+	@echo "   - Time estimate and AI token usage"
+	@echo "   - One paragraph work summary"
+	@echo ""
+	@echo "💡 Tip: New entries are added to the top for reverse chronological order"
diff --git a/ProjectDiary.md b/ProjectDiary.md
new file mode 100644
index 00000000..74aaad75
--- /dev/null
+++ b/ProjectDiary.md
@@ -0,0 +1,18 @@
+# MarkiTect Project Diary
+
+This diary tracks major work packages, events, and milestones in the MarkiTect project development. Each entry documents progress, contributors, and resources utilized.
+
+---
+
+## 2025-09-22: Repository Infrastructure & Development Workflow Establishment
+
+**Progress:** Comprehensive development infrastructure setup with automated workflows
+**Contributors:** User (bernd.worsch), Claude Code (Sonnet 4)
+**Time Estimate:** ~4-5 hours of active development
+**AI Resources:** ~50-60 Claude Sonnet 4 conversations, estimated 150K+ tokens
+
+Established complete development infrastructure for the MarkiTect project including sophisticated Makefile automation, git workflow management, and comprehensive project documentation. Key achievements include upstream repository synchronization with automatic submodule handling, intelligent virtual environment detection and management, and creation of structured project documentation system. Implemented git submodule workflow for wiki integration, created ProjectStatusDigest.md for ongoing project state documentation, and established this ProjectDiary.md for historical tracking. The Makefile now provides 15+ development targets covering setup, testing, building, maintenance, and documentation workflows. Added venv-status functionality that accurately detects shell activation state across different working directory contexts. Set up two-terminal development workflow with one for Claude Code automation and another for manual verification. This session transforms the basic prototype into a professional development environment with proper tooling, documentation, and collaborative workflows ready for team development.
+
+---
+
+*Each entry is added to the top of this file to maintain reverse chronological order. Use `make add-diary-entry` to append new entries.*
\ No newline at end of file