This book contains the papers of the 12th Advances in Computer Games C- ference (ACG 2009) held in Pamplona, Spain. The conference took place during th th May 11 13,2009 in conjunction with the 13 Computer Olympiad and the 16 World Computer Chess Championship. The Advances in Computer Games conference series is a major international forum for researchers and developers interested in all aspects of arti?cial int- ligence and computer game playing. The Pamplona conference was de?nitively characterized by fresh ideas for a large variety of games. The Program Committee (PC) received 41...