Ajax (Asynchronous JavaScript And Xml), term coined by Jesse James Garret of adaptive path. Ajax is not a new technology but it’s a web development technique for creating interactive web applications. Ajax is used to exchange small amount of data with server behind the  scenes, so that the entire web pages does not have to be reloaded each time when user makes a change. AJAX programming is centered around the XMLHTTPRequest () Object. This is the piece that makes all AJAX programming possible. Unfortunately, creating the XMLHTTPRequest () object is different for each browser.

Internet Explorer uses an ActiveX object to create its XMLHttpRequst object:

Var myRequest = new ActiveXObject (”Microsoft.XMLHTTP”);

While Mozilla/FireFox and Safari use a native object:

           Var myRequest = new XMLHttpRequest ();

Here are the basic technologies involved in Ajax applications:· XHTML (or HTML) and CSS, for marking up and styling information.

· The DOM accessed with a client-side scripting language, especially ECMAScript implementations such as JavaScript and JScript, to dynamically display and interact with the information presented.

· The XMLHttpRequest object is used to exchange data asynchronously with the web server. In some Ajax frameworks and in certain situations, an IFrame object is used instead of the XMLHttpRequest object to exchange data with the web server, and in other implementations, dynamically added