diff --git a/auth.php b/auth.php
index 9439184..7526790 100644
--- a/auth.php
+++ b/auth.php
@@ -384,6 +384,42 @@ function findUserByEmail($email) {
     return null;
 }
 
+function generateRegistrationCode() {
+    return str_pad((string) random_int(0, 999999), 6, '0', STR_PAD_LEFT);
+}
+
+function savePendingRegistration($username, $email, $password, $code) {
+    if (session_status() === PHP_SESSION_NONE) {
+        session_start();
+    }
+
+    $_SESSION['pending_registration'] = [
+        'username' => trim((string) $username),
+        'email' => trim((string) $email),
+        'password' => (string) $password,
+        'code' => (string) $code,
+        'createdAt' => time(),
+    ];
+
+    return true;
+}
+
+function getPendingRegistration() {
+    if (session_status() === PHP_SESSION_NONE) {
+        session_start();
+    }
+
+    return $_SESSION['pending_registration'] ?? null;
+}
+
+function clearPendingRegistration() {
+    if (session_status() === PHP_SESSION_NONE) {
+        session_start();
+    }
+
+    unset($_SESSION['pending_registration']);
+}
+
 function createUser($username, $password, $role = 'user', $email = '') {
     $username = trim((string) $username);
     $email = trim((string) $email);
diff --git a/default.php b/default.php
index 0de2b0f..8aeb983 100644
--- a/default.php
+++ b/default.php
@@ -5,6 +5,7 @@ define('OLLAMA_URL', 'http://127.0.0.1:11434');
 define('GUEST_USER_ENABLED', true);
 define('GUEST_USERNAME', 'guest');
 define('DEFAULT_MODEL', 'llama3.2:latest');
+define('ALLOW_REGISTRATION', true);
 
 define('MAIL_FROM', getenv('MAIL_FROM') ?: 'noreply@kai.local');
 define('MAIL_FROM_NAME', getenv('MAIL_FROM_NAME') ?: 'KaI');
diff --git a/login.php b/login.php
index dd053e4..1206162 100644
--- a/login.php
+++ b/login.php
@@ -17,30 +17,55 @@ if ($_SERVER['REQUEST_METHOD'] === 'POST') {
         exit;
     }
 
-    $username = trim($_POST['username'] ?? '');
-    $password = (string) ($_POST['password'] ?? '');
+    if (($_POST['action'] ?? '') === 'register' && ALLOW_REGISTRATION) {
+        $regUsername = trim((string) ($_POST['register_username'] ?? ''));
+        $regEmail = trim((string) ($_POST['register_email'] ?? ''));
+        $regPassword = (string) ($_POST['register_password'] ?? '');
+        $regConfirmPassword = (string) ($_POST['register_confirm_password'] ?? '');
 
-    if ($username === '' || $password === '') {
-        $errors[] = 'Please enter both username and password.';
-    } else {
-        $user = findUserByUsername($username);
-        if ($user && verifyPassword($password, $user['passwordHash'] ?? '')) {
+        if ($regUsername === '' || $regPassword === '' || $regConfirmPassword === '') {
+            $errors[] = 'Please enter a username and password for registration.';
+        } elseif ($regPassword !== $regConfirmPassword) {
+            $errors[] = 'Passwords do not match.';
+        } elseif (filter_var($regEmail, FILTER_VALIDATE_EMAIL) === false && $regEmail !== '') {
+            $errors[] = 'Please enter a valid email address.';
+        } elseif (createUser($regUsername, $regPassword, 'user', $regEmail)) {
             $_SESSION['auth_user'] = [
-                'username' => $user['username'],
-                'role' => $user['role'] ?? 'user'
+                'username' => $regUsername,
+                'role' => 'user'
             ];
 
-            if (!empty($_POST['remember'])) {
-                setRememberMeCookie($user['username']);
-            } else {
-                clearRememberMeCookie($user['username']);
-            }
-
             header('Location: index.php');
             exit;
+        } else {
+            $errors[] = 'Registration failed. The username or email may already be in use.';
         }
+    } else {
+        $username = trim($_POST['username'] ?? '');
+        $password = (string) ($_POST['password'] ?? '');
+
+        if ($username === '' || $password === '') {
+            $errors[] = 'Please enter both username and password.';
+        } else {
+            $user = findUserByUsername($username);
+            if ($user && verifyPassword($password, $user['passwordHash'] ?? '')) {
+                $_SESSION['auth_user'] = [
+                    'username' => $user['username'],
+                    'role' => $user['role'] ?? 'user'
+                ];
+
+                if (!empty($_POST['remember'])) {
+                    setRememberMeCookie($user['username']);
+                } else {
+                    clearRememberMeCookie($user['username']);
+                }
 
-        $errors[] = 'Invalid username or password.';
+                header('Location: index.php');
+                exit;
+            }
+
+            $errors[] = 'Invalid username or password.';
+        }
     }
 }
 
@@ -87,6 +112,7 @@ if (empty(loadUsers())) {
             </form>
         <?php endif; ?>
         <form method="post">
+            <input type="hidden" name="action" value="login">
             <label for="username">Username</label>
             <input id="username" name="username" required>
 
@@ -100,6 +126,12 @@ if (empty(loadUsers())) {
 
             <button type="submit">Sign in</button>
         </form>
+        <?php if (ALLOW_REGISTRATION): ?>
+            <div class="small" style="margin-top:16px;">No account yet?</div>
+            <div style="margin-top:8px;">
+                <a href="register.php" style="color:#89b4fa; font-weight:bold; text-decoration:none;">Create a new account</a>
+            </div>
+        <?php endif; ?>
         <?php if (!empty($errors)): ?>
             <div class="error">
                 <?php echo htmlspecialchars(implode('<br>', $errors)); ?>