This article focuses on simulation of computer games. The game developers are turning to serious algorithms from the computer science research community to bring their virtual worlds to ever higher levels of sophistication. Most video games completely embrace physical control and simulation. Interactivity-the key factor differentiating games from other forms of entertainment will demand it. The interactivity and choice of what to do and where to go that players will increasingly have in games means the computer has to be able to generate consistent results from an infinite variety of inputs. Many hurdles have to be overcome before games convincingly simulate physical environments and human beings. Explosions, objects tumbling, and other easy-to-simulate effects will continue to raise the quality of computer games until the day game characters are completely interactive and physically reactive to their worlds.