In this first part of the three part series, Bilal Haidar introduces Client Application Services (CLAS) that shipped with Visual Studio 2008 and .NET 3.5. These services allow Windows Forms and Windows Presentation Foundation applications to access ASP.NET 2.0 AJAX 1.0 Extensions Application Services. He begins with a brief introduction followed by a detailed discussion of ASP.NET 2.0, AJAX Extensions 1.0, and Client Application Services. He concludes the article by providing a list of classes used for CLAS.