Microsoft has introduced WPF(Windows Presentation Foundation) API in .NET3.0 framework for the first time. WPF merged all the unrelated APIs into a single unified object model. So if you want to use 3D graphics or multimedia for your application you do not use to need use different APIs. WPF provides all the functionalities you need to develop richer GUI applications.
Using WPF we can develop GUI for both windows application and web application.