From http://www.microsoft.com/en-us/download/details.aspx?id=883

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.

•ASP.NET AJAX enables you to take full advantage of the capabilities of the browser to deliver richer Web experiences that work on any modern browser


•ASP.NET AJAX enables ASP.NET developers to enrich their existing Web applications with incredible ease


•ASP.NET AJAX includes a rich client-side JavaScript framework that enables easy creation and reuse of script components and rich client-side behaviors.


•ASP.NET AJAX makes it super easy to consume services from ASP.NET and to build composite applications from services on the programmable Web.


There is additional information at http://en.wikipedia.org/wiki/ASP.NET_AJAX

>Could someone - who knows - explain to me, what specifically is "ASP.NET Ajax client-side framework"? Is it a particular .js file? if so, which one?
>
>TIA.