This article traces the formation of attachment theory to the pioneering research program of Bowlby and his colleagues at the Tavistock Clinic between 1948 and 1956. Through a discussion of the concepts and practices that informed Bowlby's program, I examine the efforts of his team to reconstruct psychoanalytic objects according to preventive objectives and operational criteria. I discuss how the exploratory techniques that Bowlby and his colleagues were developing during these years ultimately led to the establishment of a hybrid investigative framework, in which the prophylactic requirements of mental hygiene, the psychometric model of personality disturbances, the psychoanalytic theory of object relations, and a direct‐observational methodology were brought to bear on the problem of the psychological consequences of early separation experiences. I further claim that this shift in investigative practice was crucial for the succeeding theoretical developments that eventually gave rise to the statistically validated constructs of attachment theory.