This book was first published in 1984, as the revised edition of a 1979 original. The text is composed of studies in a descending sequence from perfect rationality, through imperfect and problematical rationality, to irrationality. Specifically human rationality is characterized by its capacity to relate strategically to the future, in contrast to the myopic ‘gradient climbing’ of natural selection. There is trenchant analysis of some of the parallels proposed in this connection between the biological and the social sciences. In the chapter on imperfect rationality the crucial notion is that of ‘binding oneself’, as Ulysses did before setting out to the Sirens, when weakness of will may prevent us from using our capacity for perfect rationality. The second half of the book deals with rational-actor theory, comparing its logical power and success to rival approaches, and with the varieties of irrationality expressed in contradictory beliefs and desires.