ASP.NET AJAX ,formerly code-named Atlas, is a set of extensions to ASP.NET developed by Microsoft for implementing Ajax functionality.

Including both client-side and server-side components, ASP.NET AJAX allows the developer to create web applications in ASP.NET 2.0 (and to a limited extent in other environments) which can update data on the web page without a complete reload of the page. The key technology which enables this functionality is the XMLHttpRequest object, along with Javascript and DHTML.

ASP.NET AJAX was released as a standalone extension to ASP.NET in January 2007 after a lengthy period of beta-testing. It was subsequently included with version 3.5 of the .NET Framework, which was released alongside Visual Studio 2008 in November 2007.

The core technology builds upon the same concept as Anthem.NET, which is one of the earliest serious implementations of WYSIWYG ASP.NET Ajax Technology. After an Ajax request, the HTML within some portions o