Multiple Forms in same page ASP.net MVC

You can solve this with three actions and a complex model.

 public class LoginOrRegisterViewModel
 {
      public Models.RegisterViewModel Register { get; set; }
      public Models.LoginViewModel Login { get; set; }
 }


 [HttpGet]
 public ActionResult Login()
 {
      return View("Login", new LoginOrRegisterViewModel());
 }

 [HttpPost]
 public ActionResult Register(Models.LoginViewModel model)
 {
      if(!ModelState.IsValid)
           return View("Login", new LoginOrRegisterViewModel(){ Register = model });
      else
      {
           //TODO: Validate the user
           //TODO: Write a FormsAuth ticket
           //TODO: Redirect to somewhere
     }
 }

 [HttpPost]
 public ActionResult Login(Models.RegistrationViewModel model)
 {
      if(!ModelState.IsValid)
           return View("Login", new LoginOrRegisterViewModel(){ Login = model});
      else
      {
           //TODO: CRUD for registering user
           //TODO: Write forms auth ticket
           //TODO: Redirect
     }
 }

In your code, make sure that you set the action of the Form:

 @model Models.LoginOrRegisterViewModel

 @using(Html.BeginForm("Login", "Controller", FormMethod.Post, new { id = "loginForm"}))
 {
       @Html.EditorFor(m => Model.Login)
 }

 @using(Html.BeginForm("Register", "Controller", FormMethod.Post, new { id = "registerForm"}))
 {
       @Html.EditorFor(m => Model.Register)
 }