Masterson was among the first to bring the psychoanalytic approach known as object relations theory, together with child development theory, to bear on the study of personality disorder. In so doing, he helped widen the lens through which disturbance in mental health is viewed, seeing beyond the classical Freudian approach, which is limited to neurotic symptomatology. In work he began in the mid-20th century, Masterson came to believe that the origin and treatment of personality disorders starts with understanding the formation of self and relationship that begins in the first three years of life—the so-called preOedipal period. During this time, the mother's loving support of the child's emerging self is critical for healthy psychic maturation. The psychoanalysts Otto F. Kernberg, Ronald Fairbairn, D.W. Winnicott and Heinz Kohut also played seminal roles in developing the concept of personality disorder.