One of Bowlby’s main reasons for re-casting psychoanalysis in the language of Attachment Theory was the hope that this would make it more open to empirical testing. This hope has been fully justified. The past half Century has seen an explosion of research into infant and child development, much of which was stimulated by the work of Bowlby and Mary Ainsworth. The aim of this chapter is to show how these findings point to a remarkably consistent story about the emergence of personality, or ‘attachment style’, out of the matrix of interactions between infant and care-givers in the early months and years of life. The issue of how what starts as interaction becomes internalised as personality is a key question for developmental psychology. Object-Relations Theory rests on the assumption that early relationships are a formative influence on character. My hope is to demonstrate how Bowlby’s movement away from psychoanalysis has come full circle and produced ideas that are highly relevant to, and provide strong support and enrichment for the psychoanalytic perspective.