He was a prominent American psychiatrist and psychoanalytic theorist, specializing in infant development, on which he had written a number of books — most notably The Interpersonal World of the Infant(1985). He was an honorary professor in Psychology at the University of Geneva, adjunct professor in the department of Psychiatry at the Cornell University Medical School and a lecturer at the Columbia University Center for Psychoanalytic Training and Research. He held Honorary Doctorates at the Universities of Copenhagen, Denmark; Palermo, Italy; Mons Hainaut, Belgium; Alborg, Denmark; Padua, Italy; Stockholm University, Sweden.