ViewBag/ViewData Lifecycle

The data you put in the ViewBag/ViewData is only available during the life-cycle of the request within which you populated it. MVC does not have post backs. If you need something to persist over more than a single request, you should use Session.

Here is a decent article about the differences between ViewData, ViewBag, and TempData: http://rachelappel.com/when-to-use-viewbag-viewdata-or-tempdata-in-asp.net-mvc-3-applications

From MSDN - ViewBag: The dynamic view data dictionary, ViewData: The dictionary for the view data.

So these/this is a dictionary for a given view. You set its values in your action and you use it in your view. As Zach said it's not coming back with the subsequent request. You can send its values back to any given action as a form field, in querystring, etc, but these values won't be automatically available as VieBag's properties.