This volume is concerned with the concept of rationality and the interrelations between rationality, belief and desire in the explanation and evaluation of human action. The book is conceived and structured to represent some of the most important general differences of approach to these problems, and also to connect them with problems about the relation of individual to social behaviour which are of central interest to historians, social theorists and ecomists as well as to philosophers. The essays have all been commissioned for this volume and have t appeared elsewhere. The idea for the book arose from the meetings of philosophers and social scientists sponsored by the Thyssen Foundation, and is therefore a continuation of the informal series begun by C. Hookway and P. Pettit (eds.) Action and Interpretation (C. U. P. 1978).