After installing the ASP.NET MVC Telerik Extensions, we couldn’t get the custom htmlhelpers working when using the Razor syntax. Finally we discovered that the namespace was added to the root web.config <add namespace="Telerik.Web.Mvc.UI" /> were it should have been added in the ~/Views/Web.Config: <system.web.webPages.razor> <host factoryType="System.Web.Mvc.MvcWebRazorHostFactory, System.Web.Mvc, Version=3.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" /> <pages pageBaseType="System.Web.Mvc.WebViewPage"> <namespaces> <add namespace="System.Web.Mvc" /> <add namespace="System.Web.Mvc.Ajax" /> <add namespace="System.Web.Mvc.Html" /> <add namespace="System.Web.Routing" /> <add namespace="Telerik.Web.Mvc.UI" /> </namespaces> </pages> </system.web.webPages.razor> ...