"Psychiatry...is the study of processes that involve or go on between people. The field of psychiatry is the field of interpersonal relations, under any and all circumstances in which these relations exist." This is the thesis set forth by Harry Stack Sullivan in Conceptions of Modern Psychiatry--the book that first expressed the central ideas of his theory of personality. Through his development of the theory, he made not only a vital contribution in the treatment of mental disorder--in particular, schizophrenia--but he opened an entirely new approach to the study of human personality. In the view of many analysts, he made the most original contribution to psychiatry since Freud. Roll May has said: "As Freud was the prophet for our schizoid age--our age of unrelatedness, in which, beneath all the chatter of radio and newspapers and all the multitudes of 'contacts', people are often strangers to each other."