Since the early seventies, following the pioneering work by Leo Hurwicz, economists have been studying the relationship between socially optimal goals and private self-interest. The task was to reconcile the Utopian and Hobbesian traditions, using game theory to find ways to organise the society that are both socially optimal and incentive compatible. This book provides a succinct and up-to-date account of this vast literature and will be welcomed by students, lecturers and anyone wishing to update their knowledge of the field.