50 Classics is a 11-book series with 11 primary works first released in 2003 with contributions by Tom Butler-Bowdon, Angela Duckworth, Gary Keller, Cheryl Richardson, Brian Tracy, Anthony Robbins, Robert G. Allen, Guy Kawasaki, Jerrold Mundis, Marsha Sinetar, Tom Butler Bowdon, Paul Krugman, and Stephen J. Dubner.