This book constitutes the thoroughly refereed post-proceedings of the 4th International Conference on Computers and Games, CG 2004, held in July 2004. The 21 revised full papers presented together with one keynote article were carefully selected during two rounds of reviewing and improvement from 37 submissions. The papers cover all aspects of artificial intelligence in computer-game playing. Topics addressed include evaluation and learning, search, single-agent search and planning, and computer Go.