This book maps an aspect of children's social development that has been neglected in psychological research, namely, their acquisition of the capability to participate in economic transactions. In their everyday life, children exchange a variety of goods with their peers. Girls and boys frequently trade cards, marbles, candies, as well as immaterial goods such as score values and gestures of friendship. This book is about children as exchange agents. It attempts to describe the process through which children acquire the capability to participate in commercial transactions. We present a collection of empirical studies and a review of extant literature in the area to delineate a general picture of the development of children as exchange agents.