Drupal Books

There are lots of sites online offering Free PDF Downloads of these many great Drupal books (and even some videos that people have for sale).

While you certainly can quite easily find those options they are not really a sustainable choice for the community as a whole. The book authors get paid based on the number of books sold, so downloading the copies of the book (if you haven't purchased the book) decreases the revenue for publishers and the payments to authors and overall decreases for Drupal book options in the long run.

There are lots of great free resources like the handbook on drupal.org and if you look at the revisions there it is often the case that the people who are ultimately paid to write Drupal books got their start and continue to play a big role in writing documentation that is available for free.