This document provides an introduction to XML and AJAX. It defines XML as a data representation language used to transport and store data, not for displaying. XML is used to separate data from HTML and simplify data sharing, transport, and availability across different platforms and clients. The document also introduces XMLHttpRequest, a JavaScript class that allows making HTTP requests to exchange data with a server behind the scenes. This enables updating parts of a page without reloading and sending data to a server in the background, as demonstrated in examples accessing an XML file and creating a login module using AJAX.