Economic theory has focused almost exclusively on how humans compete with each other in their economic activity, culminating in general equilibrium (Walras) and game theory (Nash). Cooperation in economic activity is, however, important, and is virtually ignored. Because our models influence our view of the world, this theoretical lacuna biases economists’ interpretation of economic behavior. Here, I propose models that provide micro-foundations for how cooperation is decentralized by economic agents. It is wrong, in particular, to view competition as decentralized and cooperation as organized only by central diktat. My approach is not to alter preferences, which is the strategy behavioral economists have adopted to produce cooperation, but...