I have the following form on an .NET MVC View:

<form method="post" enctype="multipart/form-data" action="/Video/UploadDocument"> 
<input type="file" id="document1" name="document1"/> 
<input type="submit"  value="Save"/> 
</form> 

And the controller has the following signature that gets called:

public ActionResult UploadDocument(HttpPostedFileBase file) {
    return View();
}

When I break inside the UploadDocument method, the parameter 'file' is null. I've selected a valid document on my desktop and know it contains text. What am I missing to get this file upload working?