AJAX features in ASP.NET enable you to quickly create Web pages that include a rich user experience with responsive and familiar user interface (UI) elements. AJAX features include client-script libraries that incorporate cross-browser ECMAScript (JavaScript) and dynamic HTML (DHTML) technologies, and integration with the ASP.NET server-based development platform. By using AJAX features, you can improve the user experience and the efficiency of your Web applications.

you build an Ajax application, you provide your users with a richer and more responsive user experience. You can use Ajax features to enhance server-based ASP.NET Web Forms applications by using server-side ASP.NET controls, such as the UpdatePanel control.

Why Use Microsoft Ajax Features?

Web Forms applications that use Ajax features offer the following features:
Familiar interactive UI elements such as progress indicators, tooltips, and pop-up windows.
Improved efficiency for Web Forms application, because significant parts of a Web page's processing can be performed in the browser.
Partial-page updates that refresh only the parts of the Web page that have changed.
Client integration with ASP.NET application services for forms authentication, roles, and user profiles.
Auto-generated proxy classes that simplify calling Web service methods from client script.
The ability to customize server controls to include client capabilities.
Support for the most popular browsers, which includes Microsoft Internet Explorer, Mozilla Firefox, and Apple Safari.