Windows Identity Foundation (WIF) is the core framework for building claims-based identity-aware applications using the Microsoft's Identity and Access Management paradigm. This chapter covers the aspects of programming claims in the .NET Framework 4.0 based applications using the WIF runtime and the Software Development Kit (SDK) . The runtime provides a layer of abstraction on the WS-Trust and WS-Federation security specifications and exposes the classes and the methods that help implement claims-based identity within and across the trust realms with ease. In addition, this chapter also focuses on implementing the claims-based authentication and authorization in the ASP.NET MVC 3 Web Applications and the Windows Communication Foundation (WCF) 4.0 services.