Natural resources are governed by polycentric systems, which can be conceptualized as an “ecology of games” in which policy actors participate in multiple policy forums governing interdependent issues. This article analyzes why actors perceive different payoffs across the forums in which they participate, ranging from mutually beneficial games of cooperation to conflictual zero‐sum games in which one actor's gain means another actor's loss. The authors develop hypotheses at the level of the individual, the forum, and the overall polycentric system and test them using survey data collected in three research sites: Tampa Bay, Florida; the Paraná River delta, Argentina; and the Sacramento–San Joaquin River delta, California. The empirical findings suggest that levels of conflict in policy forums are higher when the actors who participate in them are concerned with hot‐button issues, when the forums have large and diverse memberships, and in systems with a long history of conflict. The results shed new light on the drivers of conflict and cooperation in complex governance systems and suggest ways to manage conflict.