Harry Stack Sullivan (1892-1949) was the founder of the interpersonal theory of psychiatry, which focuses on interpersonal relationships and the effects of the individual's social and cultural environment on inner life, rather than on innate drives. It can be seen to complement the theories of object relations, self psychology, and psychosocial development. A complex and at times personally difficult man, Sullivan's very important contribution to psychoanalysis, psychology, and social science has not so far received the attention it deserves. In this comprehensive reassessment, F. Barton Evans explicates and critiques Sullivan's theory of personality development over the life cycle, his view of psychopathology, and his detailed exploration of the psychiatric interview as it relates to interpersonal psychotherapy.