Studies of sexual selection, interspecific mutualism, and intraspecific cooperation show that individuals exchange commodities to their mutual benefit. The exchange values of commodities are a source of conflict, and behavioral mechanisms such as partner choice and contest between competitors determines the composition of trading pairs or groups. These "biological markets" can be examined to gain a better understanding of the underlying principles of evolutionary ecology. In this volume scientists from different disciplines combine insights from economics, evolutionary biology, and the social sciences to look at comparative aspects of economic behavior in humans and other animals.