The meaning of the concept of projective identification (PI) is examined in an effort to determine the mechanisms involved in its operation. Formulations of the concept are reviewed conceiving of the process of PI as a form of unconscious affective communication. Difficulties and ambiguities of the concept are discussed, including the lack of a satisfactory explanation for unconscious communication. Possible mechanisms and processes that might contribute to the process are explored, including on one hand nonconscious and automatic neurophysiological, physiological, neuromuscular, and autonomic processes, along with mechanisms of emotional simulation, and on the other unconscious and conflictual defensive psychological processes involving aspects of projection and introjection. An attempt is made to integrate these findings in a coherent theoretical model of PI that is comprehensible in psychoanalytically meaningful and cogent terms.