THERE are two types of cooperation. In one, it makes sense to talk about individual acts of cooperation. In the other, the basic unit is a cooperative pattern of behavior – an ensemble of acts of cooperation. Cleaning up litter in the park or paying one's taxes are examples of the first. These are acts that benefit others, even if nobody else cooperates. The Living Flag illustrates the second. If a single individual went out in the street with, say, a red cap on his head, it would not benefit anyone. It takes a substantial number of people to form anything that looks like a flag pattern. This is cooperation in the literal, everyday sense, in which it means cooperating with other people – joining hands with them and walking alongside them. Or consider the cooperation of workers and capital owners in production. Labor alone or capital alone will not produce any value. To do so, they must interact in production. Benefits from division of labor is a further example. A firm that specializes in printing books will be unproductive unless there is another firm that specializes in typesetting. In this chapter I consider cooperation in this second, interactive sense.