We provide a general definition of mixed-initiative for application to the area of computer games. This definition is used to provide a survey of the ways in which mixed-initiative has been applied to games up to this point, and where and how mixed-initiative could be applied to improve the quality of games in the future. The need for algorithmic content creation though mixed-initiative interactions is demonstrated, and the application of mixed-initiative interactions to the challenge of developing realistic interactions with computer-controlled agents in an open-ended role-playing game is analyzed.