diff --git a/DEVELOPMENT_PLAN.md b/DEVELOPMENT_PLAN.md
index 14f595f..b9aa534 100644
--- a/DEVELOPMENT_PLAN.md
+++ b/DEVELOPMENT_PLAN.md
@@ -575,9 +575,101 @@ pip install pyinstaller
 
 ---
 
-## Phase 4: Professional Features (Weeks 9-12)
+## Phase 4: Professional Features & Auto-Update (Weeks 9-12)
 
-### 4.1 Enhanced Logging & Monitoring
+### 4.1 Auto-Update System with Forgejo Integration
+
+**Forgejo Configuration:**
+```
+Host: https://git.him-tools.de
+Organization: HIM-public
+Repository: webdrop-bridge
+API Endpoint: https://git.him-tools.de/api/v1/repos/HIM-public/webdrop-bridge
+```
+
+**Tasks:**
+
+#### 4.1.1 Update Manager (`src/webdrop_bridge/core/updater.py`)
+
+```python
+class UpdateManager:
+    """Manages auto-updates via Forgejo releases."""
+    
+    def __init__(self, config: Config):
+        self.forgejo_url = "https://git.him-tools.de"
+        self.repo = "HIM-public/webdrop-bridge"
+        self.current_version = config.app_version
+    
+    async def check_for_updates(self) -> Optional[Release]:
+        """Query Forgejo API for latest release.
+        
+        Returns:
+            Release info if newer version available, None otherwise
+        """
+        # GET https://git.him-tools.de/api/v1/repos/HIM-public/webdrop-bridge/releases/latest
+        # Compare version semantic versioning
+        
+    async def download_update(self, release: Release) -> Path:
+        """Download MSI/DMG from Forgejo release artifacts.
+        
+        Args:
+            release: Release information from API
+            
+        Returns:
+            Path to downloaded installer file
+        """
+        # Download from release assets
+        # Verify checksums
+        
+    def install_update(self, installer_path: Path) -> bool:
+        """Launch installer and schedule restart.
+        
+        Args:
+            installer_path: Path to MSI or DMG file
+            
+        Returns:
+            True if installation scheduled, False otherwise
+        """
+```
+
+**Configuration** (`.env`):
+```env
+# Auto-Update Settings
+FORGEJO_URL=https://git.him-tools.de
+FORGEJO_REPO=HIM-public/webdrop-bridge
+AUTO_UPDATE_CHECK=true
+AUTO_UPDATE_INTERVAL=86400  # 24 hours in seconds
+AUTO_UPDATE_NOTIFY=true
+```
+
+**Features:**
+- Check on startup (with 24h cache)
+- Manual "Check for Updates" menu option
+- Background download (non-blocking)
+- User notification with changelog
+- Automatic restart capability
+- Rollback to previous version (optional)
+- Security: HTTPS-only, checksum verification
+
+**Deliverables:**
+- [ ] `src/webdrop_bridge/core/updater.py` - Update manager
+- [ ] Menu item for manual update check
+- [ ] Update notification dialog
+- [ ] Unit tests for update checking and downloading
+- [ ] Integration with Forgejo API
+
+**Acceptance Criteria:**
+- Can query Forgejo releases API
+- Detects new versions correctly
+- Downloads and verifies checksums
+- Prompts user for restart
+- Manual check works from menu
+- Gracefully handles network errors
+- Version comparison uses semantic versioning
+
+---
+
+### 4.2 Enhanced Logging & Monitoring
 
 **Deliverables:**
 - [ ] Structured logging (JSON format option)
@@ -587,7 +679,7 @@ pip install pyinstaller
 
 ---
 
-### 4.2 Advanced Configuration
+### 4.3 Advanced Configuration
 
 **Deliverables:**
 - [ ] UI settings dialog
@@ -597,7 +689,7 @@ pip install pyinstaller
 
 ---
 
-### 4.3 User Documentation
+### 4.4 User Documentation
 
 **Deliverables:**
 - [ ] User manual (PDF, HTML)
@@ -609,26 +701,16 @@ pip install pyinstaller
 
 ## Phase 5: Post-Release (Months 2-3)
 
-### 5.1 Auto-Update System
+### 5.1 Analytics & Monitoring
 
 **Requirements:**
-- Check for updates on startup
-- Download in background
-- Staged rollout support
-- Rollback capability
-
----
-
-### 5.2 Analytics & Monitoring
-
-**Metrics:**
 - App usage statistics
 - Error/crash reporting
 - Feature usage tracking
 
 ---
 
-### 5.3 Community Support
+### 5.2 Community Support
 
 **Channels:**
 - GitHub Issues
@@ -665,6 +747,8 @@ pip install pyinstaller
 - PyInstaller (building)
 - Sphinx (documentation)
 - pytest (testing)
+- aiohttp (auto-update downloads)
+- packaging (version comparison)
 
 ---
 
@@ -681,6 +765,7 @@ webdrop-bridge/
 │   │   ├── __init__.py
 │   │   ├── validator.py        ← Path validation
 │   │   ├── drag_interceptor.py ← Drag handling
+│   │   ├── updater.py          ← Auto-update system (Phase 4)
 │   │   └── errors.py           ← Custom exceptions
 │   ├── ui/
 │   │   ├── __init__.py