This article seeks to improve our understanding of policy institutions and cooperation by adaptingLong's (1958)analysis of the ecology of games to the context of collaborative land use and transportation planning in California. The traditional institutional rational choice analysis argues that collaborative institutions reduce the transaction costs of cooperation among multiple policy actors. The ecology of games framework extends IRC by emphasizing the consequences of multiple institutions and identifies several reasons why collaborative institutions may actually reduce the amount of cooperation in existing policy venues. Analyses of survey data from policy actors in five California regions demonstrate that higher levels of cooperation in collaborative institutions are associated with lower levels of cooperation in other land-use and transportation planning institutions.