Introduction to WAI ARIA
http://dev.opera.com/articles/view/introduction-to-wai-aria/

Lemon, Gez
Opera
2008

Abstract:

This article is for those who are new to ARIA. You need an understanding of HTML and the potential difficulties that people with disabilities can face using the Web. It is useful to be familiar with some Rich Internet Applications from a user's perspectiveAfter reading this article, you'll understand what ARIA is for, how to integrate it into your sites, and how you can use it now to make even the simplest of sites more accessible.