Philosophers, social scientists, and laymen have used two perspectives in analying social action. One sees mans action as the result of causal forces, and the other sees action as purposive and goal directed. Mathematical treatment of social action has shown this same dichotomy. Some models of behavior describe a causal process, in which there is no place for intention or purpose. Most stochastic models of behavior, whether individual or group, are like this. Another body of work, however, employs purpose, anticipation of some future state, and action designed to maximie the proximity to some goal. Classical microeconomic theory, statistical decision theory, and game theory exemplify this direction. The Mathematics of Collective Action examines these two directions of work, and makes original contributions to the second.