The present research tests the idea that playing a team-player video game in which players work together as teammates and assist each other in achieving a common goal increases cooperative behavior toward a new partner. In fact, relative to a single-player mode, cooperatively playing a video game increased cooperation in a mixed-motive decision dilemma task. Because the players were exposed to the same video game content in both experimental conditions, the effect on cooperative behavior can only be accounted for by the different way the game was played. Mediation analyses revealed that cooperative team play promoted feelings of cohesion, which activated trust (i.e., the expectation of reciprocal cooperation), which in turn increased cooperative behavior. Copyright © 2013 John Wiley & Sons, Ltd.