Assembly used to define MVC is " System.Web.MVC" For more detail have a look of the linkhttps://msdn.microsoft.com/en-us/library/dd566232%28v=vs.100%29.aspx

"System.Web.Mvc" assembly

The MVC framework is defined through System.Web.Mvc assembly.

MVC framework defined through System.Web.Mvc

System.Web.MVC

System.web.MVC

using System.Web.Mvc;

System.Web.Mvc

If it is prior to ASP.NET Core then System.Web.Mvc

"System.Web.Mvc" assembly

System.Web.Mvc

System.Web.MVC

The MVC framework is defined through System.Web.MVC.assembly

System.Web.mvc

System.Web.Mvc

System.Web.Mvc assembly contains all classes and interfaces to support ASP.NET MVC Framework

System.Web.Mvc

System.Web.Mvc

Namespace: System.Web.Mvc Assembly: System.Web.Mvc (in System.Web.Mvc.dll)

System.Web.Mvc