AJAX (Asynchronous JavaScript and XML), or Ajax, is a group of inter-related web development techniques used for creating interactive web applications. A primary characteristic is the increased responsiveness and interactivity of web pages achieved by exchanging small amounts of data with the server "behind the scenes" so that the entire web page does not have to be reloaded each time there is a need to fetch data from the server. This is intended to increase the web page's interactivity, speed, functionality, and usability.

AJAX is asynchronous in that extra data is requested from the server and loaded in the background without interfering with the display and behavior of the existing page. JavaScript is the scripting language in which AJAX function calls are typically made. Data is retrieved using the XMLHttpRequest object that is available to scripting languages run in modern browsers, or alternatively Remote Scripting in browsers that do not support XMLHttpRequest. There is, however, no requirement that the asynchronous content be formatted in XML.

AJAX is a cross-platform technique usable on many different operating systems, computer architectures, and web browsers as it is based on open standards such as JavaScript and the DOM. There are free and open source implementations of suitable frameworks and libraries.

Constituent technologies

AJAX uses a combination of:

XHTML (or HTML) and CSS, for marking up and styling information.

The DOM accessed with a client-side scripting language, particularly 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