diff --git a/dashboard/habits.html b/dashboard/habits.html
index 554bd0f..aec0859 100644
--- a/dashboard/habits.html
+++ b/dashboard/habits.html
@@ -853,6 +853,15 @@
         function showAddHabitModal() {
             const modal = document.getElementById('habitModal');
             const form = document.getElementById('habitForm');
+            const modalTitle = document.querySelector('.modal-title');
+            const submitBtnText = document.getElementById('submitBtnText');
+            
+            // Reset editing state
+            editingHabitId = null;
+            
+            // Reset modal title and button text to create mode
+            modalTitle.textContent = 'Add Habit';
+            submitBtnText.textContent = 'Create Habit';
             
             // Reset form
             form.reset();
@@ -877,6 +886,9 @@
         function closeHabitModal() {
             const modal = document.getElementById('habitModal');
             modal.classList.remove('active');
+            
+            // Reset editing state
+            editingHabitId = null;
         }
         
         // Close modal when clicking outside
@@ -1004,6 +1016,9 @@
             const submitBtn = document.getElementById('submitHabitBtn');
             const submitBtnText = document.getElementById('submitBtnText');
             
+            // Determine if we're creating or editing
+            const isEditing = editingHabitId !== null;
+            
             // Get form values
             const name = document.getElementById('habitName').value.trim();
             const category = document.getElementById('habitCategory').value;
@@ -1061,11 +1076,14 @@
             
             // Show loading state
             submitBtn.disabled = true;
-            submitBtnText.textContent = 'Creating...';
+            submitBtnText.textContent = isEditing ? 'Saving...' : 'Creating...';
             
             try {
-                const response = await fetch('/echo/api/habits', {
-                    method: 'POST',
+                const url = isEditing ? `/echo/api/habits/${editingHabitId}` : '/echo/api/habits';
+                const method = isEditing ? 'PUT' : 'POST';
+                
+                const response = await fetch(url, {
+                    method: method,
                     headers: {
                         'Content-Type': 'application/json'
                     },
@@ -1078,16 +1096,16 @@
                 }
                 
                 // Success
-                showToast('Habit created successfully!', 'success');
+                showToast(isEditing ? 'Habit updated!' : 'Habit created successfully!', 'success');
                 closeHabitModal();
                 await loadHabits();
                 
             } catch (error) {
-                console.error('Failed to create habit:', error);
-                showToast('Failed to create habit: ' + error.message, 'error');
+                console.error(`Failed to ${isEditing ? 'update' : 'create'} habit:`, error);
+                showToast(`Failed to ${isEditing ? 'update' : 'create'} habit: ` + error.message, 'error');
             } finally {
                 submitBtn.disabled = false;
-                submitBtnText.textContent = 'Create Habit';
+                submitBtnText.textContent = isEditing ? 'Save Changes' : 'Create Habit';
             }
         }
         
@@ -1108,9 +1126,71 @@
             }, 3000);
         }
         
-        // Show edit habit modal (placeholder)
+        // Show edit habit modal
+        let editingHabitId = null; // Track which habit we're editing
+        
         function showEditHabitModal(habitId) {
-            alert('Edit Habit modal - coming in next story!');
+            const habit = habits.find(h => h.id === habitId);
+            if (!habit) {
+                showToast('Habit not found', 'error');
+                return;
+            }
+            
+            editingHabitId = habitId;
+            
+            const modal = document.getElementById('habitModal');
+            const form = document.getElementById('habitForm');
+            const modalTitle = document.querySelector('.modal-title');
+            const submitBtn = document.getElementById('submitHabitBtn');
+            const submitBtnText = document.getElementById('submitBtnText');
+            
+            // Change modal title and button text
+            modalTitle.textContent = 'Edit Habit';
+            submitBtnText.textContent = 'Save Changes';
+            
+            // Pre-populate form fields
+            document.getElementById('habitName').value = habit.name;
+            document.getElementById('habitCategory').value = habit.category || 'health';
+            document.getElementById('habitPriority').value = habit.priority || 3;
+            document.getElementById('habitNotes').value = habit.notes || '';
+            document.getElementById('frequencyType').value = habit.frequency?.type || 'daily';
+            document.getElementById('reminderTime').value = habit.reminderTime || '';
+            
+            // Set selected color and icon
+            selectedColor = habit.color || '#3B82F6';
+            selectedIcon = habit.icon || 'dumbbell';
+            
+            // Initialize color picker with current selection
+            initColorPicker();
+            
+            // Initialize icon picker with current selection
+            initIconPicker();
+            
+            // Update frequency params and pre-populate
+            updateFrequencyParams();
+            
+            // Pre-populate frequency params based on type
+            const frequencyType = habit.frequency?.type;
+            if (frequencyType === 'specific_days' && habit.frequency.days) {
+                const dayCheckboxes = document.querySelectorAll('input[name="day"]');
+                dayCheckboxes.forEach(cb => {
+                    cb.checked = habit.frequency.days.includes(parseInt(cb.value));
+                });
+            } else if (frequencyType === 'x_per_week' && habit.frequency.count) {
+                const xPerWeekInput = document.getElementById('xPerWeek');
+                if (xPerWeekInput) {
+                    xPerWeekInput.value = habit.frequency.count;
+                }
+            } else if (frequencyType === 'custom' && habit.frequency.interval) {
+                const customIntervalInput = document.getElementById('customInterval');
+                if (customIntervalInput) {
+                    customIntervalInput.value = habit.frequency.interval;
+                }
+            }
+            
+            // Show modal
+            modal.classList.add('active');
+            lucide.createIcons();
         }
         
         // Delete habit (placeholder)
diff --git a/dashboard/tests/test_habits_frontend.py b/dashboard/tests/test_habits_frontend.py
index 7961dcb..4bedc5d 100644
--- a/dashboard/tests/test_habits_frontend.py
+++ b/dashboard/tests/test_habits_frontend.py
@@ -3,6 +3,7 @@ Test suite for Habits frontend page structure and navigation
 Story US-006: Frontend - Page structure, layout, and navigation link
 Story US-007: Frontend - Habit card component
 Story US-008: Frontend - Create habit modal with all options
+Story US-009: Frontend - Edit habit modal
 """
 
 import sys
@@ -417,17 +418,18 @@ def test_client_side_validation():
     print("✓ Test 28: Client-side validation checks name required")
 
 def test_submit_posts_to_api():
-    """Test 29: Submit sends POST /echo/api/habits and refreshes list"""
+    """Test 29: Submit sends POST /echo/api/habits (or PUT for edit) and refreshes list"""
     habits_path = Path(__file__).parent.parent / 'habits.html'
     content = habits_path.read_text()
     
     assert 'submitHabitForm' in content, "Should have submitHabitForm function"
     
     submit_func = content[content.find('function submitHabitForm'):]
-    assert "fetch('/echo/api/habits'" in submit_func or 'fetch("/echo/api/habits"' in submit_func, \
-        "Should POST to /echo/api/habits"
-    assert "'POST'" in submit_func or '"POST"' in submit_func, \
-        "Should use POST method"
+    # Check for conditional URL and method (since US-009 added edit support)
+    assert ('/echo/api/habits' in submit_func), \
+        "Should use /echo/api/habits endpoint"
+    assert ("'POST'" in submit_func or '"POST"' in submit_func or "'PUT'" in submit_func or '"PUT"' in submit_func), \
+        "Should use POST or PUT method"
     assert 'JSON.stringify' in submit_func, "Should send JSON body"
     assert 'loadHabits()' in submit_func, "Should refresh habit list on success"
     
@@ -508,6 +510,244 @@ def test_typecheck_us008():
     
     print("✓ Test 33: Typecheck passes (all modal functions defined)")
 
+def test_edit_modal_opens_on_gear_icon():
+    """Test 34: Clicking gear icon on habit card opens edit modal"""
+    habits_path = Path(__file__).parent.parent / 'habits.html'
+    content = habits_path.read_text()
+    
+    # Check that gear icon exists with onclick handler
+    assert 'settings' in content, "Should have settings icon (gear)"
+    assert "showEditHabitModal" in content, "Should have showEditHabitModal function call"
+    
+    # Check that showEditHabitModal function is defined and not a placeholder
+    assert 'function showEditHabitModal(habitId)' in content, "showEditHabitModal should be defined"
+    assert 'editingHabitId = habitId' in content or 'editingHabitId=habitId' in content, \
+        "Should set editingHabitId"
+    assert 'const habit = habits.find(h => h.id === habitId)' in content or \
+           'const habit=habits.find(h=>h.id===habitId)' in content, \
+        "Should find habit by ID"
+    
+    print("✓ Test 34: Edit modal opens on gear icon click")
+
+def test_edit_modal_prepopulated():
+    """Test 35: Edit modal is pre-populated with all existing habit data"""
+    habits_path = Path(__file__).parent.parent / 'habits.html'
+    content = habits_path.read_text()
+    
+    # Check that form fields are pre-populated
+    assert "getElementById('habitName').value = habit.name" in content or \
+           "getElementById('habitName').value=habit.name" in content, \
+        "Should pre-populate habit name"
+    assert "getElementById('habitCategory').value = habit.category" in content or \
+           "getElementById('habitCategory').value=habit.category" in content, \
+        "Should pre-populate category"
+    assert "getElementById('habitPriority').value = habit.priority" in content or \
+           "getElementById('habitPriority').value=habit.priority" in content, \
+        "Should pre-populate priority"
+    assert "getElementById('habitNotes').value = habit.notes" in content or \
+           "getElementById('habitNotes').value=habit.notes" in content, \
+        "Should pre-populate notes"
+    assert "getElementById('frequencyType').value = habit.frequency" in content or \
+           "getElementById('frequencyType').value=habit.frequency" in content, \
+        "Should pre-populate frequency type"
+    
+    # Check color and icon selection
+    assert 'selectedColor = habit.color' in content or 'selectedColor=habit.color' in content, \
+        "Should set selectedColor from habit"
+    assert 'selectedIcon = habit.icon' in content or 'selectedIcon=habit.icon' in content, \
+        "Should set selectedIcon from habit"
+    
+    print("✓ Test 35: Edit modal pre-populated with habit data")
+
+def test_edit_modal_title_and_button():
+    """Test 36: Modal title shows 'Edit Habit' and button shows 'Save Changes'"""
+    habits_path = Path(__file__).parent.parent / 'habits.html'
+    content = habits_path.read_text()
+    
+    # Check that modal title is changed to Edit Habit
+    assert "modalTitle.textContent = 'Edit Habit'" in content or \
+           'modalTitle.textContent="Edit Habit"' in content or \
+           "modalTitle.textContent='Edit Habit'" in content, \
+        "Should set modal title to 'Edit Habit'"
+    
+    # Check that submit button text is changed
+    assert "submitBtnText.textContent = 'Save Changes'" in content or \
+           'submitBtnText.textContent="Save Changes"' in content or \
+           "submitBtnText.textContent='Save Changes'" in content, \
+        "Should set button text to 'Save Changes'"
+    
+    print("✓ Test 36: Modal title shows 'Edit Habit' and button shows 'Save Changes'")
+
+def test_edit_modal_frequency_params():
+    """Test 37: Frequency params display correctly for habit's current frequency type"""
+    habits_path = Path(__file__).parent.parent / 'habits.html'
+    content = habits_path.read_text()
+    
+    # Check that updateFrequencyParams is called
+    assert 'updateFrequencyParams()' in content, "Should call updateFrequencyParams()"
+    
+    # Check that frequency params are pre-populated for specific types
+    assert 'specific_days' in content and 'habit.frequency.days' in content, \
+        "Should handle specific_days frequency params"
+    assert 'x_per_week' in content and 'habit.frequency.count' in content, \
+        "Should handle x_per_week frequency params"
+    assert 'custom' in content and 'habit.frequency.interval' in content, \
+        "Should handle custom frequency params"
+    
+    # Check that day checkboxes are pre-populated
+    assert 'cb.checked = habit.frequency.days.includes' in content or \
+           'cb.checked=habit.frequency.days.includes' in content, \
+        "Should pre-select days for specific_days frequency"
+    
+    print("✓ Test 37: Frequency params display correctly for current frequency")
+
+def test_edit_modal_icon_color_pickers():
+    """Test 38: Icon and color pickers show current selections"""
+    habits_path = Path(__file__).parent.parent / 'habits.html'
+    content = habits_path.read_text()
+    
+    # Check that pickers are initialized after setting values
+    assert 'initColorPicker()' in content, "Should call initColorPicker()"
+    assert 'initIconPicker()' in content, "Should call initIconPicker()"
+    
+    # Check that selectedColor and selectedIcon are set before initialization
+    showEditIndex = content.find('function showEditHabitModal')
+    initColorIndex = content.find('initColorPicker()', showEditIndex)
+    selectedColorIndex = content.find('selectedColor = habit.color', showEditIndex)
+    
+    assert selectedColorIndex > 0 and selectedColorIndex < initColorIndex, \
+        "Should set selectedColor before calling initColorPicker()"
+    
+    print("✓ Test 38: Icon and color pickers show current selections")
+
+def test_edit_modal_submit_put():
+    """Test 39: Submit sends PUT /echo/api/habits/{id} and refreshes list on success"""
+    habits_path = Path(__file__).parent.parent / 'habits.html'
+    content = habits_path.read_text()
+    
+    # Check that editingHabitId is tracked
+    assert 'let editingHabitId' in content or 'editingHabitId' in content, \
+        "Should track editingHabitId"
+    
+    # Check that isEditing is determined
+    assert 'const isEditing = editingHabitId !== null' in content or \
+           'const isEditing=editingHabitId!==null' in content or \
+           'isEditing = editingHabitId !== null' in content, \
+        "Should determine if editing"
+    
+    # Check that URL and method are conditional
+    assert "const url = isEditing ? `/echo/api/habits/${editingHabitId}` : '/echo/api/habits'" in content or \
+           'const url=isEditing?`/echo/api/habits/${editingHabitId}`' in content or \
+           "url = isEditing ? `/echo/api/habits/${editingHabitId}` : '/echo/api/habits'" in content, \
+        "URL should be conditional based on isEditing"
+    
+    assert "const method = isEditing ? 'PUT' : 'POST'" in content or \
+           "const method=isEditing?'PUT':'POST'" in content or \
+           "method = isEditing ? 'PUT' : 'POST'" in content, \
+        "Method should be conditional (PUT for edit, POST for create)"
+    
+    # Check that loadHabits is called after success
+    assert 'await loadHabits()' in content, "Should refresh habit list after success"
+    
+    print("✓ Test 39: Submit sends PUT and refreshes list")
+
+def test_edit_modal_toast_messages():
+    """Test 40: Toast shown for success and error"""
+    habits_path = Path(__file__).parent.parent / 'habits.html'
+    content = habits_path.read_text()
+    
+    # Check for conditional success message
+    assert "isEditing ? 'Habit updated!' : 'Habit created successfully!'" in content or \
+           "isEditing?'Habit updated!':'Habit created successfully!'" in content, \
+        "Should show different toast message for edit vs create"
+    
+    # Check that error toast handles both edit and create
+    assert 'Failed to ${isEditing' in content or 'Failed to ' + '${isEditing' in content, \
+        "Error toast should be conditional"
+    
+    print("✓ Test 40: Toast messages for success and error")
+
+def test_edit_modal_add_resets_state():
+    """Test 41: showAddHabitModal resets editingHabitId and modal UI"""
+    habits_path = Path(__file__).parent.parent / 'habits.html'
+    content = habits_path.read_text()
+    
+    # Find showAddHabitModal function
+    add_modal_start = content.find('function showAddHabitModal()')
+    add_modal_end = content.find('function ', add_modal_start + 1)
+    add_modal_func = content[add_modal_start:add_modal_end]
+    
+    # Check that editingHabitId is reset
+    assert 'editingHabitId = null' in add_modal_func or 'editingHabitId=null' in add_modal_func, \
+        "showAddHabitModal should reset editingHabitId to null"
+    
+    # Check that modal title is reset to 'Add Habit'
+    assert "modalTitle.textContent = 'Add Habit'" in add_modal_func or \
+           'modalTitle.textContent="Add Habit"' in add_modal_func, \
+        "Should reset modal title to 'Add Habit'"
+    
+    # Check that button text is reset to 'Create Habit'
+    assert "submitBtnText.textContent = 'Create Habit'" in add_modal_func or \
+           'submitBtnText.textContent="Create Habit"' in add_modal_func, \
+        "Should reset button text to 'Create Habit'"
+    
+    print("✓ Test 41: showAddHabitModal resets editing state")
+
+def test_edit_modal_close_resets_state():
+    """Test 42: closeHabitModal resets editingHabitId"""
+    habits_path = Path(__file__).parent.parent / 'habits.html'
+    content = habits_path.read_text()
+    
+    # Find closeHabitModal function
+    close_modal_start = content.find('function closeHabitModal()')
+    close_modal_end = content.find('function ', close_modal_start + 1)
+    close_modal_func = content[close_modal_start:close_modal_end]
+    
+    # Check that editingHabitId is reset when closing
+    assert 'editingHabitId = null' in close_modal_func or 'editingHabitId=null' in close_modal_func, \
+        "closeHabitModal should reset editingHabitId to null"
+    
+    print("✓ Test 42: closeHabitModal resets editing state")
+
+def test_edit_modal_no_console_errors():
+    """Test 43: No obvious console error sources in edit modal code"""
+    habits_path = Path(__file__).parent.parent / 'habits.html'
+    content = habits_path.read_text()
+    
+    # Check for common error patterns
+    assert content.count('getElementById(') > 0, "Should use getElementById"
+    
+    # Check that habit is validated before use
+    showEditIndex = content.find('function showEditHabitModal')
+    showEditEnd = content.find('\n        }', showEditIndex + 500)  # Find end of function
+    showEditFunc = content[showEditIndex:showEditEnd]
+    
+    assert 'if (!habit)' in showEditFunc or 'if(!habit)' in showEditFunc, \
+        "Should check if habit exists before using it"
+    assert 'showToast' in showEditFunc and 'error' in showEditFunc, \
+        "Should show error toast if habit not found"
+    
+    print("✓ Test 43: No obvious console error sources")
+
+def test_typecheck_us009():
+    """Test 44: Typecheck passes - all edit modal functions and variables defined"""
+    habits_path = Path(__file__).parent.parent / 'habits.html'
+    content = habits_path.read_text()
+    
+    # Check that editingHabitId is declared
+    assert 'let editingHabitId' in content, "editingHabitId should be declared"
+    
+    # Check that showEditHabitModal is fully implemented (not placeholder)
+    assert 'function showEditHabitModal(habitId)' in content, "showEditHabitModal should be defined"
+    assert 'alert' not in content[content.find('function showEditHabitModal'):content.find('function showEditHabitModal')+1000], \
+        "showEditHabitModal should not be a placeholder with alert()"
+    
+    # Check that submitHabitForm handles both create and edit
+    assert 'const isEditing' in content or 'isEditing' in content, \
+        "submitHabitForm should determine if editing"
+    
+    print("✓ Test 44: Typecheck passes (edit modal fully implemented)")
+
 def run_all_tests():
     """Run all tests in sequence"""
     tests = [
@@ -547,9 +787,21 @@ def run_all_tests():
         test_toast_notifications,
         test_modal_no_console_errors,
         test_typecheck_us008,
+        # US-009 tests
+        test_edit_modal_opens_on_gear_icon,
+        test_edit_modal_prepopulated,
+        test_edit_modal_title_and_button,
+        test_edit_modal_frequency_params,
+        test_edit_modal_icon_color_pickers,
+        test_edit_modal_submit_put,
+        test_edit_modal_toast_messages,
+        test_edit_modal_add_resets_state,
+        test_edit_modal_close_resets_state,
+        test_edit_modal_no_console_errors,
+        test_typecheck_us009,
     ]
     
-    print(f"\nRunning {len(tests)} frontend tests for US-006, US-007, and US-008...\n")
+    print(f"\nRunning {len(tests)} frontend tests for US-006, US-007, US-008, and US-009...\n")
     
     failed = []
     for test in tests: