Competing organizations are often defined by their niche overlap or structural equivalence in resource dependence, but the very structure that defines competitors can also identify cooperators. There is a fine line between competition and cooperation, but current theories give insufficient guidance as to which will take place and also contribute to the belief that cooperation between competitors is illegitimate. We show that the legitimacy of these practices, as well the evaluation of their welfare implications, are context bound. Individuals and societies that have been influenced by different theories of competition could reasonably (and have) reach different conclusions as to the legitimacy of competitor cooperation. We then critique extant ideas as to when competitors will cooperate, which rely on industry structure, and suggest instead that perception and social identity are more important in tipping the cooperate–compete balance. We conclude by showing how our arguments inform an important current stream of management research, on the process of institutional change.