-All the namespaces and classes used for ASP.NET MVC reside in the System.Web.Mvc assembly.

-System.Web.Mvc namespace

This namespace provides classes and interfaces that support the MVC pattern for ASP.NET Web applications. This namespace also contains classes that manage controllers, controller factories, partial views, action results, views and model binders.

-System.Web.Mvc.Ajax namespace

This namespace provides classes that support Ajax scripts in an ASP.NET MVC application. The namespace also provides support of Ajax scripts and Ajax option settings.

-System.Web.Mvc.Async namespace

This namespace provides classes and interfaces that support asynchronous actions in an ASP.NET MVC application.

-System.Web.Mvc.Html namespace

This namespace provides classes that help in rendering HTML controls in an MVC application. The namespace contains classes providing forms, input controls, links, partial views, and validation support.