ASP.NET MVC uses the namespace classes that as follows:

-System.Web.Mvc namespace: this consists of classes and interfaces that follows MVC pattern to create web applications. This includes the controllers, libraries, actions, views, models.

-System.Web.Mvc.Ajax namespace: this consists of classes that support the AJAX scripts and used in the web applications. This also include the AJAX related settings and options.

-System.Web.Mvc.Async namespace: this consists of classes and interfaces that provide asynchronous actions in the web applications.

-System.Web.Mvc.Html namespace: this consists of classes in the form of helper application and follows the MVC pattern. This includes the forms, controls, links, views and validations.