The Gathering 4 Gardner is a biannual conference founded--and for many years organized--by Tom Rodgers to celebrate the spirit of Martin Gardner. While primarily concerned with recreational mathematics, most of Gardner's intellectual interests are featured, including magic, literature, philosophy, puzzles, art, and rationality. Gardner's writing inspired several generations of mathematicians by introducing us to the joy of discovery and exploration, and the Gathering's aim is to continue that tradition of inspiration. This volume, a tribute to Rodgers and Gardner, consists of papers...