diff --git a/package-lock.json b/package-lock.json
index 515883b..3c07216 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -2050,6 +2050,16 @@
         "@types/node": "*"
       }
     },
+    "node_modules/@types/cookie-parser": {
+      "version": "1.4.10",
+      "resolved": "https://registry.npmjs.org/@types/cookie-parser/-/cookie-parser-1.4.10.tgz",
+      "integrity": "sha512-B4xqkqfZ8Wek+rCOeRxsjMS9OgvzebEzzLYw7NHYuvzb7IdxOkI0ZHGgeEBX4PUM7QGVvNSK60T3OvWj3YfBRg==",
+      "dev": true,
+      "license": "MIT",
+      "peerDependencies": {
+        "@types/express": "*"
+      }
+    },
     "node_modules/@types/cookiejar": {
       "version": "2.1.5",
       "resolved": "https://registry.npmjs.org/@types/cookiejar/-/cookiejar-2.1.5.tgz",
@@ -3127,6 +3137,25 @@
         "node": ">= 0.6"
       }
     },
+    "node_modules/cookie-parser": {
+      "version": "1.4.7",
+      "resolved": "https://registry.npmjs.org/cookie-parser/-/cookie-parser-1.4.7.tgz",
+      "integrity": "sha512-nGUvgXnotP3BsjiLX2ypbQnWoGUPIIfHQNZkkC668ntrzGWEZVW70HDEB1qnNGMicPje6EttlIgzo51YSwNQGw==",
+      "license": "MIT",
+      "dependencies": {
+        "cookie": "0.7.2",
+        "cookie-signature": "1.0.6"
+      },
+      "engines": {
+        "node": ">= 0.8.0"
+      }
+    },
+    "node_modules/cookie-parser/node_modules/cookie-signature": {
+      "version": "1.0.6",
+      "resolved": "https://registry.npmjs.org/cookie-signature/-/cookie-signature-1.0.6.tgz",
+      "integrity": "sha512-QADzlaHc8icV8I7vbaJXJwod9HWYp8uCqf1xa4OfNu1T7JVxQIrUgOWtHdNDtPiywmFbiS12VjotIXLrKM3orQ==",
+      "license": "MIT"
+    },
     "node_modules/cookie-signature": {
       "version": "1.0.7",
       "resolved": "https://registry.npmjs.org/cookie-signature/-/cookie-signature-1.0.7.tgz",
@@ -7875,6 +7904,7 @@
         "@flashcard/shared": "*",
         "bcryptjs": "^3.0.3",
         "better-sqlite3": "^11.0.0",
+        "cookie-parser": "^1.4.7",
         "drizzle-orm": "^0.33.0",
         "express": "^4.19.0",
         "multer": "^1.4.5-lts.1",
@@ -7885,6 +7915,7 @@
       "devDependencies": {
         "@types/bcryptjs": "^2.4.6",
         "@types/better-sqlite3": "^7.6.0",
+        "@types/cookie-parser": "^1.4.10",
         "@types/express": "^4.17.0",
         "@types/multer": "^1.4.0",
         "@types/node": "^20.0.0",
diff --git a/packages/backend/package.json b/packages/backend/package.json
index 87d10f9..4fd88eb 100644
--- a/packages/backend/package.json
+++ b/packages/backend/package.json
@@ -19,6 +19,7 @@
     "@flashcard/shared": "*",
     "bcryptjs": "^3.0.3",
     "better-sqlite3": "^11.0.0",
+    "cookie-parser": "^1.4.7",
     "drizzle-orm": "^0.33.0",
     "express": "^4.19.0",
     "multer": "^1.4.5-lts.1",
@@ -29,6 +30,7 @@
   "devDependencies": {
     "@types/bcryptjs": "^2.4.6",
     "@types/better-sqlite3": "^7.6.0",
+    "@types/cookie-parser": "^1.4.10",
     "@types/express": "^4.17.0",
     "@types/multer": "^1.4.0",
     "@types/node": "^20.0.0",
diff --git a/packages/backend/src/lib/cookies.ts b/packages/backend/src/lib/cookies.ts
new file mode 100644
index 0000000..ae37f56
--- /dev/null
+++ b/packages/backend/src/lib/cookies.ts
@@ -0,0 +1,34 @@
+import type { CookieOptions } from 'express';
+
+export const SID_COOKIE = 'flashcard_sid';
+export const CSRF_COOKIE = 'flashcard_csrf';
+export const CSRF_HEADER = 'x-csrf-token';
+
+export function sidCookieOptions(expiresAtSec: number): CookieOptions {
+  return {
+    httpOnly: true,
+    sameSite: 'lax',
+    secure: process.env.COOKIE_SECURE === 'true',
+    path: '/',
+    expires: new Date(expiresAtSec * 1000),
+  };
+}
+
+export function csrfCookieOptions(expiresAtSec: number): CookieOptions {
+  return {
+    httpOnly: false,
+    sameSite: 'lax',
+    secure: process.env.COOKIE_SECURE === 'true',
+    path: '/',
+    expires: new Date(expiresAtSec * 1000),
+  };
+}
+
+export function clearCookieOptions(): CookieOptions {
+  return {
+    httpOnly: true,
+    sameSite: 'lax',
+    secure: process.env.COOKIE_SECURE === 'true',
+    path: '/',
+  };
+}
diff --git a/packages/backend/src/middleware/csrf.ts b/packages/backend/src/middleware/csrf.ts
new file mode 100644
index 0000000..400ce4f
--- /dev/null
+++ b/packages/backend/src/middleware/csrf.ts
@@ -0,0 +1,25 @@
+import { randomBytes } from 'node:crypto';
+import type { Request, Response, NextFunction } from 'express';
+import { CSRF_COOKIE, CSRF_HEADER, csrfCookieOptions } from '../lib/cookies.js';
+import { ApiError } from '../lib/errors.js';
+
+const SAFE_METHODS = new Set(['GET', 'HEAD', 'OPTIONS']);
+
+export function ensureCsrfToken(req: Request, res: Response, next: NextFunction): void {
+  if (!req.cookies?.[CSRF_COOKIE]) {
+    const token = randomBytes(24).toString('base64url');
+    const expires = Math.floor(Date.now() / 1000) + 30 * 24 * 60 * 60;
+    res.cookie(CSRF_COOKIE, token, csrfCookieOptions(expires));
+  }
+  next();
+}
+
+export function verifyCsrf(req: Request, _res: Response, next: NextFunction): void {
+  if (SAFE_METHODS.has(req.method)) return next();
+  const cookieToken = req.cookies?.[CSRF_COOKIE];
+  const headerToken = req.headers[CSRF_HEADER];
+  if (!cookieToken || !headerToken || cookieToken !== headerToken) {
+    return next(new ApiError(403, 'CSRF_MISMATCH', 'CSRF token mismatch'));
+  }
+  next();
+}