Sullivan was one of the most influential American psychiatrists active in the early twentieth century. His contributions included establishing a standard method for psychiatric interviews and demonstrating the importance of milieu and psychosocial interventions in the care of first-break schizophrenic patients. He was also one of the founders of interpersonal psychoanalysis, emphasizing the importance of psychosocial forces in shaping personality development and in the pathogenesis of psychiatric illnesses. His uncanny aptitude in working with psychotic patients was linked to his lifelong struggle with homosexual impulses and addiction problems. His profound sense of “marginality” may have been rooted in his difficult childhood, growing up as the only child in an Irish catholic family isolated in a protestant rural New England town. The chapter also includes a brief discussion of the long struggle of mental health professionals toward “depathologizing” homosexuality.