If you're looking for the guide to web accessibility, then (as of this writing) this is the bible of it. However, at 600+ pages of dense material, it's a slog to get through. However, persistent readers will be rewarded with the knowledge of the entire landscape of web accessibility, from how to make HTML, CSS, JavaScript, Flash, and PDFs accessible, to the inner reasonings behind the WCAG and Section 508. And, if you need to know how to make your site conform to the accessible laws and guidelines of the United States, Australia, Italy, the European Union, etc. or what the Flanders Plan for Accessible Websites or the what the Japanese JIS X 8341-3 Standard is all about, then this is the book for you.