I would like to use this preface to thank some persons and institutions which have been important during the various stages of writing this book. First of all, I am grateful to Kluwer Academic Publishers for giving me the opportunity to write this book. I started writing the book in 1998 while I was working at the Departament d'Economia i d'Historia Economica at Universidad Autonoma de Barcelona, and continued the writing job from september 1998 to september 2000 at the Departamento de Economfa at Universidad Carlos III de Madrid. The book has been completed while I was visiting the Department of Quantitative Economics at the University of Maastricht from october 2000 to august 2001. I wish to thank these three departments for their hospitality. The book has improved substantially by comments and critique from the following persons who have read parts of the manuscript: Geir Asheim, Eric van Damme, Janos Flesch, Mari-Angeles de Frutos, Diego Moreno, Hans Peters, Antonio Romero and Dries Vermeulen. I should also mention my discussions with Peter Wakker about the decision-theoretic foundations of noncooperative game theory, which have had an important impact on various parts of the book. Finally, I wish to express my warmest gratitude to my parents, my brother and my sister, and, last but not least, to Cati, to whom I dedicate this book.

. This major new book will be of particular interest not only to philosophers but to decision theorists, political scientists, economists, and researchers in artificial intelligence.

The first textbook to explain the principles of epistemic game theory.

Rationality has long been a central topic in philosophy, crossing standard divisions and categories. It continues to attract much attention in published research and teaching by philosophers as well as scholars in other disciplines, including economics, psychology, and law. The Oxford Handbook of Rationality is an indispensable reference to the current state of play in this vital and interdisciplinary area of study. Twenty-two newly commissioned chapters by a roster of distinguished philosophers provide an overview of the prominent views on rationality, with each author also developing a unique and distinctive argument.

Groups of people perform acts that are subject to standards of rationality. A committee may sensibly award fellowships, or may irrationally award them in violation of its own policies. A theory of collective rationality defines collective acts that are evaluable for rationality and formulates principles for their evaluation. This book argues that a group's act is evaluable for rationality if it is the products of acts its members fully control. It also argues that such an act is collectively rational if the acts of the group's members are rational. Efficiency is a goal of collective rationality, but not a requirement, except in cases where conditions are ideal for joint action and agents have rationally prepared for joint action. The people engaged in a game of strategy form a group, and the combination of their acts yields a collective act. If their collective act is rational, it constitutes a solution to their game. A theory of collective rationality yields principles concerning solutions to games. One principle requires that a solution constitute an equilibrium among the incentives of the agents in the game. In a cooperative game some agents are coalitions of individuals, and it may be impossible for all agents to pursue all incentives. Because rationality is attainable, the appropriate equilibrium standard for cooperative games requires that agents pursue only incentives that provide sufficient reasons to act. The book's theory of collective rationality supports an attainable equilibrium-standard for solutions to cooperative games and shows that its realization follows from individuals' rational acts. By extending the theory of rationality to groups, this book reveals the characteristics that make an act evaluable for rationality and the way rationality's evaluation of an act responds to the type of control its agent exercises over the act. The book's theory of collective rationality contributes to philosophical projects such as contractarian ethics and to practical projects such as the design of social institutions.

This major contribution to game theory offers this conception of equilibrium in games: strategic equilibrium.