The essays in this volume consider the question of whether the self is a unity or whether it should be conceived without metaphor as divided - as a 'multiple self'. The issue is a central one for several disciplines. It bears directly on the account of rationality and the explanation of individual decision-making and behaviour. Is the hypothesis of a multiple self required to deal with the problems of self-deception and weakness of will; and can the conceptual tools developed in the study of interpersonal conflict be applied to the analysis of intra-personal struggle? Most of the essays, by a number of leading philosophers, psychologists and economists, appear here for the first time. They bring out the interdisciplinary importance of the question, and will interest readers in all those areas. The volume will also usefully supplement The Foundations of Social Choice Theory, edited by Jon Elster and Aanund Hylland, which appears in the same series and is also concerned with the foundations of rationality.