diff --git a/backend/app/User/UseCases/SignupUser/SignupUser.php b/backend/app/User/UseCases/SignupUser/SignupUser.php
index 7f2c78e..7228e87 100644
--- a/backend/app/User/UseCases/SignupUser/SignupUser.php
+++ b/backend/app/User/UseCases/SignupUser/SignupUser.php
@@ -15,6 +15,8 @@ class SignupUser
 {
     private const MIN_PASSWORD_LENGTH = 8;
 
+    private const DISPLAY_NAME_PATTERN = '/^[a-z0-9_-]{3,30}$/';
+
     public function __construct(
         private UserRepository $userRepo,
         private PasswordHasher $hasher,
@@ -29,6 +31,19 @@ class SignupUser
         if ($request->email === null || $request->email === '') {
             throw new BadRequestException('email is required');
         }
+        if ($request->displayName === null || $request->displayName === '') {
+            throw new BadRequestException('displayName is required');
+        }
+        if (
+            preg_match(
+                self::DISPLAY_NAME_PATTERN,
+                $request->displayName,
+            ) !== 1
+        ) {
+            throw new BadRequestException(
+                'displayName must be 3-30 chars of [a-z0-9_-]'
+            );
+        }
         if ($request->password === null || $request->password === '') {
             throw new BadRequestException('password is required');
         }
@@ -47,11 +62,16 @@ class SignupUser
         if ($this->userRepo->findByEmail($email) !== null) {
             throw new DomainException('email already registered');
         }
+        if ($this->userRepo->findByDisplayName($request->displayName) !== null) {
+            throw new DomainException('displayName already taken');
+        }
 
         return $this->userRepo->create(new CreateUserDto(
             email: $email,
+            displayName: $request->displayName,
             passwordHash: $this->hasher->hash($request->password),
             isAdmin: false,
+            emailConfirmedAt: null,
         ));
     }
 }
diff --git a/backend/app/User/UseCases/SignupUser/SignupUserRequest.php b/backend/app/User/UseCases/SignupUser/SignupUserRequest.php
index b6f809f..e202131 100644
--- a/backend/app/User/UseCases/SignupUser/SignupUserRequest.php
+++ b/backend/app/User/UseCases/SignupUser/SignupUserRequest.php
@@ -6,6 +6,7 @@ class SignupUserRequest
 {
     public function __construct(
         public ?string $email,
+        public ?string $displayName,
         public ?string $password,
     ) {}
 }