It is apparent that the X in AJAX stands for XML, but if you have used AJAX it is most likely that you may not have encountered XML as such anywhere in the request/response. Probably you might not have encountered use of XML because your server is not expecting an XML because as far as the server side is concerned it does not matter whether the request is synchronous or asynchronous. Its job is to serve the request and respond back. But there might be situations where the server might be expecting a XML based request. For example let’s say the server has to communicate with some web service for the response. Then if the request is in XML it saves some time and as a simple translation could be applied to frame the request to be sent to the service. Here is a part “Using XML in requests and responses” from the Mastering AJAX series from IBM developerworks that explains with example of how to use AJAX with real XML request and response.