The concepts of rationality that are used by social scientists in the formation of hypotheses, models and explanations are explored in this collection of original papers by a number of distinguished philosophers and social scientists. The aim of the book is to display the variety of the concepts used, to show the different roles they play in theories of very different kinds over a wide range of disciplines, including economics, sociology, psychology, political science and anthropology, and to assess the explanatory and predictive power that a theory can draw from such concepts.