AJAX stands for "Asynchronous JavaScript and XML." It is a technology that facilitates the development of responsive web applications. Responsive means that you can have your data refreshed without the need of full page postback which can significantly reduced bandwidth usage and faster performance. AJAX is a "cross-platform" technology and can be used across various operating systems, computer architectures and different web browsers as it is based on XML and JavaScript that are open standards. PHP, ASP.NET,ASP,JSP, Cold fusion all can integrate AJAX library into their code easily. But to use AJAX library it is not that simple and sometimes it is quite hard to code, therefore Mcrosoft has create their own set of AJAX library and named it as ATLAS. You need to download Microsoft AJAX library before you can start coding your Ajax applications. URL For downloading latest AJAX library is here