Ajax is a group of interrelated web development techniques used on the client-side to create asynchronous web applications. With Ajax, web applications can send data to, and retrieve data from, a server asynchronously (in the background) without interfering with the display and behavior of the existing page. 

Here's a collection of over fifteen Ajax Tutorials & Resources to Learn!

Ajax Daddy

Ajaxian

How to integrate Google Calendar in your website using AJAX

Ajax Tutorial

RSS Ajax Javascript Ticker Tutorial

Ajax Applications

Ajax Tutorial

Building your first Ajax application with PHP

Tutorials Point – Ajax Tutorial

Quick & Dirty Ajax

Ajax Tutorial

Ajax Tutorial – Google Code

Learn Ajax Tutorial

Creating a Dynamic Poll with jQuery and PHP

Ajax Forms with JQuery

Using Ajax to Validate Forms