diff --git a/backend/src/controllers/auth.js b/backend/src/controllers/auth.js
index a32ffea..6d2076e 100644
--- a/backend/src/controllers/auth.js
+++ b/backend/src/controllers/auth.js
@@ -10,6 +10,8 @@ const {
 const { sendVerificationEmail, sendWelcomeEmail, sendPasswordResetEmail } = require('../emails');
 const { sanitizeForEmail, timingSafeEqual } = require('../utils/sanitize');
 const securityConfig = require('../config/security');
+const { ACTIONS, log: activityLog } = require('../services/activityLog');
+const { getClientIP } = require('../utils/request');
 
 // Register new user (Phase 1.5 - with WSDC support and email verification)
 async function register(req, res, next) {
@@ -92,6 +94,20 @@ async function register(req, res, next) {
     // Generate JWT token
     const token = generateToken({ userId: user.id });
 
+    // Log registration activity
+    activityLog({
+      userId: user.id,
+      username: user.username,
+      ipAddress: getClientIP(req),
+      action: ACTIONS.AUTH_REGISTER,
+      method: req.method,
+      path: req.path,
+      metadata: {
+        email: user.email,
+        hasWsdcId: !!user.wsdcId,
+      },
+    });
+
     res.status(201).json({
       success: true,
       message: 'User registered successfully. Please check your email to verify your account.',
@@ -199,6 +215,20 @@ async function login(req, res, next) {
     // Return user without password
     const { passwordHash, ...userWithoutPassword } = user;
 
+    // Log login activity
+    activityLog({
+      userId: user.id,
+      username: user.username,
+      ipAddress: getClientIP(req),
+      action: ACTIONS.AUTH_LOGIN,
+      method: req.method,
+      path: req.path,
+      metadata: {
+        email: user.email,
+        emailVerified: user.emailVerified,
+      },
+    });
+
     res.json({
       success: true,
       message: 'Login successful',
@@ -276,6 +306,19 @@ async function verifyEmailByToken(req, res, next) {
     // Remove sensitive data
     const { passwordHash, verificationToken, verificationCode, verificationTokenExpiry, resetToken, resetTokenExpiry, ...userWithoutPassword } = updatedUser;
 
+    // Log email verification activity
+    activityLog({
+      userId: updatedUser.id,
+      username: updatedUser.username,
+      ipAddress: getClientIP(req),
+      action: ACTIONS.AUTH_VERIFY_EMAIL,
+      method: req.method,
+      path: req.path,
+      metadata: {
+        verificationMethod: 'token',
+      },
+    });
+
     res.status(200).json({
       success: true,
       message: 'Email verified successfully!',
@@ -356,6 +399,19 @@ async function verifyEmailByCode(req, res, next) {
     // Remove sensitive data
     const { passwordHash, verificationToken, verificationCode, verificationTokenExpiry, resetToken, resetTokenExpiry, ...userWithoutPassword } = updatedUser;
 
+    // Log email verification activity
+    activityLog({
+      userId: updatedUser.id,
+      username: updatedUser.username,
+      ipAddress: getClientIP(req),
+      action: ACTIONS.AUTH_VERIFY_EMAIL,
+      method: req.method,
+      path: req.path,
+      metadata: {
+        verificationMethod: 'code',
+      },
+    });
+
     res.status(200).json({
       success: true,
       message: 'Email verified successfully!',
@@ -543,6 +599,19 @@ async function resetPassword(req, res, next) {
       },
     });
 
+    // Log password reset activity
+    activityLog({
+      userId: user.id,
+      username: user.username,
+      ipAddress: getClientIP(req),
+      action: ACTIONS.AUTH_PASSWORD_RESET,
+      method: req.method,
+      path: req.path,
+      metadata: {
+        email: user.email,
+      },
+    });
+
     res.status(200).json({
       success: true,
       message: 'Password reset successfully',
diff --git a/backend/src/routes/admin.js b/backend/src/routes/admin.js
index 45f3395..3de8d2a 100644
--- a/backend/src/routes/admin.js
+++ b/backend/src/routes/admin.js
@@ -1,13 +1,16 @@
 const express = require('express');
 const { prisma } = require('../utils/db');
 const { authenticate } = require('../middleware/auth');
+const { requireAdmin } = require('../middleware/admin');
 const matchingService = require('../services/matching');
 const { SUGGESTION_STATUS } = require('../constants');
+const { ACTIONS, log: activityLog } = require('../services/activityLog');
+const { getClientIP } = require('../utils/request');
 
 const router = express.Router();
 
 // POST /api/admin/events/:slug/run-now - Trigger matching immediately for an event
-router.post('/events/:slug/run-now', authenticate, async (req, res, next) => {
+router.post('/events/:slug/run-now', authenticate, requireAdmin, async (req, res, next) => {
   try {
     const { slug } = req.params;
 
@@ -47,6 +50,23 @@ router.post('/events/:slug/run-now', authenticate, async (req, res, next) => {
         },
       });
 
+      // Log admin matching run activity
+      activityLog({
+        userId: req.user.id,
+        username: req.user.username,
+        ipAddress: getClientIP(req),
+        action: ACTIONS.ADMIN_MATCHING_RUN,
+        resource: `event:${event.id}`,
+        method: req.method,
+        path: req.path,
+        metadata: {
+          eventSlug: event.slug,
+          runId: runRow.id,
+          matchedCount,
+          notFoundCount,
+        },
+      });
+
       return res.json({
         success: true,
         data: {
@@ -74,7 +94,7 @@ router.post('/events/:slug/run-now', authenticate, async (req, res, next) => {
 });
 
 // GET /api/admin/events/:slug/matching-runs?limit=20 - List recent runs
-router.get('/events/:slug/matching-runs', authenticate, async (req, res, next) => {
+router.get('/events/:slug/matching-runs', authenticate, requireAdmin, async (req, res, next) => {
   try {
     const { slug } = req.params;
     const limit = Math.min(parseInt(req.query.limit || '20', 10), 100);
@@ -136,7 +156,7 @@ router.get('/events/:slug/matching-runs', authenticate, async (req, res, next) =
 module.exports = router;
 
 // GET /api/admin/events/:slug/matching-runs/:runId/suggestions - List suggestions created in this run
-router.get('/events/:slug/matching-runs/:runId/suggestions', authenticate, async (req, res, next) => {
+router.get('/events/:slug/matching-runs/:runId/suggestions', authenticate, requireAdmin, async (req, res, next) => {
   try {
     const { slug, runId } = req.params;
     const onlyAssigned = String(req.query.onlyAssigned || 'true') === 'true';
diff --git a/backend/src/routes/events.js b/backend/src/routes/events.js
index aa72228..329a305 100644
--- a/backend/src/routes/events.js
+++ b/backend/src/routes/events.js
@@ -4,6 +4,8 @@ const { authenticate } = require('../middleware/auth');
 const { getIO } = require('../socket');
 const matchingService = require('../services/matching');
 const { SUGGESTION_STATUS, MATCH_STATUS } = require('../constants');
+const { ACTIONS, log: activityLog } = require('../services/activityLog');
+const { getClientIP } = require('../utils/request');
 
 const router = express.Router();
 
@@ -319,6 +321,21 @@ router.post('/checkin/:token', authenticate, async (req, res, next) => {
       },
     });
 
+    // Log checkin activity
+    activityLog({
+      userId: req.user.id,
+      username: req.user.username,
+      ipAddress: getClientIP(req),
+      action: ACTIONS.EVENT_CHECKIN,
+      resource: `event:${event.id}`,
+      method: req.method,
+      path: req.path,
+      metadata: {
+        eventSlug: event.slug,
+        eventName: event.name,
+      },
+    });
+
     res.json({
       success: true,
       alreadyCheckedIn: false,
@@ -491,6 +508,21 @@ router.delete('/:slug/leave', authenticate, async (req, res, next) => {
       },
     });
 
+    // Log leave event activity
+    activityLog({
+      userId: req.user.id,
+      username: req.user.username,
+      ipAddress: getClientIP(req),
+      action: ACTIONS.EVENT_LEAVE,
+      resource: `event:${event.id}`,
+      method: req.method,
+      path: req.path,
+      metadata: {
+        eventSlug: event.slug,
+        eventName: event.name,
+      },
+    });
+
     res.json({
       success: true,
       message: 'Successfully left the event',
diff --git a/backend/src/routes/matches.js b/backend/src/routes/matches.js
index c044918..f27aae1 100644
--- a/backend/src/routes/matches.js
+++ b/backend/src/routes/matches.js
@@ -5,6 +5,8 @@ const { authenticate } = require('../middleware/auth');
 const { getIO } = require('../socket');
 const { MATCH_STATUS } = require('../constants');
 const matchingService = require('../services/matching');
+const { ACTIONS, log: activityLog } = require('../services/activityLog');
+const { getClientIP } = require('../utils/request');
 
 const router = express.Router();
 
@@ -184,6 +186,22 @@ router.post('/', authenticate, matchRequestLimiter, async (req, res, next) => {
       console.error('Failed to emit match request notification:', socketError);
     }
 
+    // Log match creation activity
+    activityLog({
+      userId: req.user.id,
+      username: req.user.username,
+      ipAddress: getClientIP(req),
+      action: ACTIONS.MATCH_CREATE,
+      resource: `match:${match.id}`,
+      method: req.method,
+      path: req.path,
+      metadata: {
+        matchSlug: match.slug,
+        targetUserId: targetUserId,
+        eventSlug: eventSlug,
+      },
+    });
+
     res.status(201).json({
       success: true,
       data: match,
@@ -778,6 +796,22 @@ router.put('/:slug/accept', authenticate, async (req, res, next) => {
     const isUser1 = updatedMatch.user1Id === userId;
     const partner = isUser1 ? updatedMatch.user2 : updatedMatch.user1;
 
+    // Log match acceptance activity
+    activityLog({
+      userId: req.user.id,
+      username: req.user.username,
+      ipAddress: getClientIP(req),
+      action: ACTIONS.MATCH_ACCEPT,
+      resource: `match:${updatedMatch.id}`,
+      method: req.method,
+      path: req.path,
+      metadata: {
+        matchSlug: updatedMatch.slug,
+        partnerId: partner.id,
+        eventSlug: updatedMatch.event.slug,
+      },
+    });
+
     res.json({
       success: true,
       data: {
@@ -867,6 +901,22 @@ router.delete('/:slug', authenticate, async (req, res, next) => {
       console.error('Failed to emit match cancelled notification:', socketError);
     }
 
+    // Log match rejection activity
+    activityLog({
+      userId: req.user.id,
+      username: req.user.username,
+      ipAddress: getClientIP(req),
+      action: ACTIONS.MATCH_REJECT,
+      resource: `match:${match.id}`,
+      method: req.method,
+      path: req.path,
+      metadata: {
+        matchSlug: match.slug,
+        eventSlug: match.event.slug,
+        matchStatus: match.status,
+      },
+    });
+
     res.json({
       success: true,
       message: 'Match deleted successfully',
diff --git a/backend/src/socket/index.js b/backend/src/socket/index.js
index d653cec..fce5242 100644
--- a/backend/src/socket/index.js
+++ b/backend/src/socket/index.js
@@ -1,6 +1,7 @@
 const { Server } = require('socket.io');
 const { verifyToken } = require('../utils/auth');
 const { prisma } = require('../utils/db');
+const { ACTIONS, log: activityLog } = require('../services/activityLog');
 
 // Track active users in each event room
 const activeUsers = new Map(); // eventId -> Set of { socketId, userId, username, avatar }
@@ -202,6 +203,20 @@ function initializeSocket(httpServer) {
           username: socket.user.username,
           avatar: socket.user.avatar,
         });
+
+        // Log join event chat activity
+        activityLog({
+          userId: socket.user.id,
+          username: socket.user.username,
+          ipAddress: socket.handshake.address,
+          action: ACTIONS.EVENT_JOIN_CHAT,
+          resource: `event:${eventId}`,
+          method: 'SOCKET',
+          path: 'join_event_room',
+          metadata: {
+            eventSlug: slug,
+          },
+        });
       } catch (error) {
         console.error('Join event room error:', error);
         socket.emit('error', { message: 'Failed to join room' });
@@ -236,6 +251,20 @@ function initializeSocket(httpServer) {
 
       console.log(`👤 ${socket.user.username} left event room ${socket.currentEventSlug}`);
 
+      // Log leave event chat activity
+      activityLog({
+        userId: socket.user.id,
+        username: socket.user.username,
+        ipAddress: socket.handshake.address,
+        action: ACTIONS.EVENT_LEAVE_CHAT,
+        resource: `event:${eventId}`,
+        method: 'SOCKET',
+        path: 'leave_event_room',
+        metadata: {
+          eventSlug: socket.currentEventSlug,
+        },
+      });
+
       // Clear current event data
       socket.currentEventId = null;
       socket.currentEventRoom = null;
@@ -349,6 +378,20 @@ function initializeSocket(httpServer) {
             where: { id: parseInt(matchId) },
             data: updateData,
           });
+
+          // Log join match room activity
+          activityLog({
+            userId: socket.user.id,
+            username: socket.user.username,
+            ipAddress: socket.handshake.address,
+            action: ACTIONS.CHAT_JOIN_ROOM,
+            resource: `match:${matchId}`,
+            method: 'SOCKET',
+            path: 'join_match_room',
+            metadata: {
+              matchId: parseInt(matchId),
+            },
+          });
         }
       } catch (error) {
         console.error('Join match room error:', error);