Three Books to Read About Processing

Actually these books you can find them at the processing webpage, with its reviews.
Of course you can get them from Amazon.

Casey Reas and Ben Fry.
Published June 2010, O'Reilly Media. 208 pages. Paperback.
Order from Amazon.

Casey Reas and Ben Fry (Foreword by John Maeda).
Published August 2007, MIT Press. 736 pages. Hardcover.Order From Amazon. 

Daniel Shiffman.
Published December 2012. PDF, Web, Paperback.
Order From Amazon.