Adding Expert Knowledge and Exploration in Monte-Carlo Tree Search -- A Lock-Free Multithreaded Monte-Carlo Tree Search Algorithm -- Monte-Carlo Tree Search in Settlers of Catan -- Evaluation Function Based Monte-Carlo LOA -- Monte-Carlo Kakuro -- A Study of UCT and Its Enhancements in an Artificial Game -- Creating an Upper-Confidence-Tree Program for Havannah -- Randomized Parallel Proof-Number Search -- Hex, Braids, the Crossing Rule, and XH-Search -- Performance and Prediction: Bayesian Modelling of Fallible Choice in Chess -- Plans, Patterns, and Move Categories Guiding a Highly Selective Search -- 6-Man Chess and Zugzwangs -- Solving Kriegspiel Endings with Brute Force: The Case of KR vs. K -- Conflict Resolution of Chinese Chess Endgame Knowledge Base -- On Drawn K-In-A-Row Games -- Optimal Analyses for 3×n AB Games in the Worst Case -- Automated Discovery of Search-Extension Features -- Deriving Concepts and Strategies from Chess Tablebases -- Incongruity-Based Adaptive Game Balancing -- Data Assurance in Opaque Computations.

This volume constitutes the thoroughly refereed post-conference proceedings of the Twelfth Advances in Computer Games Conference, ACG 2009, held in Pamplona, Spain, in May 2009. The 20 revised full papers presented were carefully reviewed and selected from 41 submissions for inclusion in the book. The topics addressed contain Monte-Carlo tree search, Bayesian modeling, selective search, brute force, conflict resolution, solving games, optimization, concept discovery, incongruity theory, and data assurance.