Learning Ajax

I know Basics of Java, Java Script and Html. I wanna learn AJAX..
which book is prefer to learn ajax?..

Please Give me some reference to understand to concept of AJAX concept...

Ajax is 'Asynchronous JavaScript and XML' - Don't ask me why XML when 'everyone' is using JSON these days... :)
So to tune your question... I guess you wish to learn JavaScript and get better at it, right?

If this is the case here are two books that are excellent:
* JavaScript: The Definitive Guide by David Flanagan - http://www.amazon.com/JavaScript-Definitive-Guide-David-Flanagan/dp/0596101996/
* JavaScript: The Good Parts by Douglas Crockford - http://www.amazon.com/dp/0596517742/

Even though it's getting a bit old, Ajax in Action is still relevant when it comes to learning the basics of Ajax. Though its use of Prototype is rather creaky (Prototype is a bit of a dinosaur these days).

There'a also Head First Ajax (which I helped to review) which is very good if you like the Head First style.

And once you want to start using it for real using jQuery, I recommend by own book (of course): jQuery in Action; chapter 8 is completely devoted to Ajax.

Also note that because, as Ido Green points out, the X in AJAX is no longer particularly relevant, most people just use it as the noun Ajax rather than the defunct acronym AJAX.