Introduction

ASP.NET AJAX, previously called "Atlas", is a Microsoft implementation of an AJAX based framework, created for ASP.NET (although it can be used on other platforms as well). AJAX stands for Asynchronous JavaScript and XML, which, very simply put, is a way of transferring data between the server and client without sending the entire page, and thereby creating a complete postback. This allows for a richer experience for the user, since loading dynamic content can be done in the background, without refreshing and redrawing the entire page. If you have ever used Gmail or Outlook Web Access, you have used an Ajax enabled webapplication, and especially Google have made Ajax very popular.

While it's perfectly possible to use Ajax without Microsoft ASP.NET AJAX, a lot of things are way easier, since Microsoft has wrapped some of most tedious parts of Ajax into their implementation. For instance, the 3 most popular browsers requires different ways of using Ajax, and have different JavaScript implementations. ASP.NET AJAX simplifies this a lot and allows you to write the same code to target all 3 major browsers.