Projective identification is the unconscious phantasy of putting split-off parts of the self into another person, who is then felt to contain them or to be them; it often evokes in that person feelings that match what was projected. Melanie Klein described it in Notes on Some Schizoid Mechanisms[1] (1946) as one of the defences of the infant's earliest phase, which she later called the paranoid-schizoid position. The concept grew out of her account of projection, presupposes splitting, and is counted among the defences.
Analysts who took up Klein's concept carried it into the treatment of psychotic and borderline patients. Herbert Rosenfeld used it in the first clinical paper to apply the new term, Hanna Segal explained disturbed symbol formation by it, and Wilfred Bion described a normal form of it as the infant's earliest means of communication. Donald Meltzer, Otto Kernberg and Thomas Ogden later distinguished its forms and motives, used it to read borderline transferences, and described it as an interpersonal process that acts on the person who receives the projection. Several later concepts derive from it, among them Segal's symbolic equation, Bion's container and contained and Ogden's analytic third.