For half a century Interpersonal psychoanalysis has developed relatively independent of the tradition of Freud and his followers. The Interpersonal movement was founded by Harry Stack Sullivan, Clara Thompson and others who believed that the psyche could not be understood as an entity that evolves without input from the external environment. The Interpersonal view is that interactions between people influence every aspect of the individual's experience, and that no person can be studied without simultaneously noting the ongoing impact between the observer and the observed. This line of thought has led to conclusions concerning personality, psychopathology and clinical technique that depart from traditional psychoanalysis. The paper illustrates a number of these differences, emphasizing that the current emergence of the “two-person model” of the psychoanalytic situation offers a potential rapprochement between the Interpersonal and more classical views.