Diekmann and Lindenberg Cooperation 1 1 July 5 th, 2000 . Forthcoming in the International Encyclopaedia of the Social Sciences. Sociological aspects of cooperation Andreas Diekmann and Siegwart Lindenberg Abstract The most prominent studies of cooperation in sociology proceed from some kind of rationality assumption. There are basically two groups of studies, one starting from the assumption of rational egoists and the other starting from the assumption of social rationality in which other regard has a prominent place. The studies based on the assumption of rational egoists is strongly inspired by (mostly game-theoretical) developments in economics and political science but add important sociological aspects to the analysis. Most important among these contributions are the dynamic analysis of cooperation, the link between formal and informal institutions, and the importance of social networks for embedding problematic transactions. Studies based on social rationality introduce assumptions on social preferences, learning, and framing. Important questions are the circumstances that strengthen or weaken social preferences; the evolution of signals and conventions that govern trust, and the effects of goals on the definition of the situation. It seems that studies using social rationality are on the rise. Sociological aspects of cooperation Andreas Diekmann and Siegwart Lindenberg 1. The problem of cooperation. Individuals cooperate if each willingly acts in a manner that contributes to the others‘ welfare. Cooperation is one of the oldest and most revered topics in sociology even though it appeared under a variety of headings, such as „social order“ and „solidarity“. The classical sociological answers to the question how cooperation among individuals comes about differ in detail but share a common core: Cooperation is the result of shared values and norms and norm- conforming behavior. A problem with this „obligation-centered“ solution is that there is no explanation of where norms come from and why the degree of norm conformity varies even for the same individual. over time. Theory that might solve these problems was not developed until the 1970s when a sea change in the basic assumptions on human action took place within sociology. At that time, analyses of cooperation among rational egoists (mostly rooted in game theory) began to shed new light on the way one might analyze cooperation, norms, and norm conforming behavior. For quite some time, game-theoretic analyses of cooperation had become the most serious attempt to explain cooperation. Big advances were made but many problems remained, especially the problem that individuals do not seem to be as self-centered