ASP.NET AJAX integrates client script libraries with the ASP.NET 2.0 server-based development framework. This new Web development technology extends ASP.NET, offering the interactive user interface benefits of AJAX with a programming model that is more familiar to ASP.NET developers, making it very easy to add AJAX to your applications quickly and with minimal effort. However, ASP.NET AJAX isn’t just for ASP.NET development. You can take advantage of the rich client framework to easily build client-centric Web applications that integrate with any backend data provider.
Microsoft, ASP.NET, AJAX