The first Banff Conference on Theoretical Psychology, which led to the establishment of the University of Alberta’s Center for Advanced Study in Theoretical Psychology, was held 9-12 April 1965, at the university’s mountain retreat in the Canadian Rockies. The aim of the conference was to take the first steps toward defining areas of common ground among diverse theories of psychology, with a view to making more integrated and comprehensive statements about behaviour. The meeting was the first phase of long-range commitment which the Center proposes to make the advancement of theoretical psychology. This was a working conference – a manifestation of the kind of activity on which the Center will focus in the years ahead. The papers presented ranged from the general-theoretical-metatheoretical statements of Royce, Rozeboom, and Galanter, through the biological viewpoint of Bartley and the systems orientation of von Bertalanffy and Frank, to the phenomenology of MacLeod and the existential outlook of the philosopher Tennessen. These papers are contained in this volume, whose major concern is to display the full spectrum of theories of psychology and at the same time, point the ways to integration. Thus, while the contributions hold no illusions regarding the idea of uniting the fragmented diversity called psychology, they are convinced that a more equitable balance between the rational and empirical will move the discipline toward unification. Feedback from the seventy auditors who attended the conference indicates that the book will interest everyone concerned with clarifying our at present chaotic understanding of behaviour. It will appeal to psychologists of all persuasions, and philosophers who are interested in the foundation of psychology. It has a great deal to offer students concerned with the theoretical and philosophical foundations of psychological behaviour theory, and the related disciplines of psychiatry, biology, anthropology, and sociology.