Besides making the first mention of the significant other in psychological literature, Sullivan developed the Self System, a configuration of the personality traits developed in childhood and reinforced by positive affirmation and the security operations developed in childhood to avoid anxiety and threats to self-esteem.
Sullivan's work on interpersonal relationships became the foundation of interpersonal psychoanalysis, a school of psychoanalytic theory and treatment that stresses the detailed exploration of the nuances of patients' patterns of interacting with others.