Mourning and Melancholia is Freud's (1917) first, and fundamental contribution to the psychoanalytic understanding of normal and pathological mourning, the psychopathology of major affective disorders and the psychodynamic determinants of depression. At the same time, it also marks major developments in psychoanalytic theory at large, particularly the early formulations of the concept of the superego, the fundamental nature of identification processes, and the role of aggression in psychopathology. There are several strikingly original and fundamental propositions in the theory of the psychopathology of depression put forth in "Mourning and Melancholia". These include the central importance of aggression turned against the self when intensely ambivalent object investments are lost; the role of the superego in this self-directed aggression; the split in the self revealed in the superego's attack on the ego, and the fusion of another part of the self with an internalized object: as the victim of that attack. In what follows, I shall attempt to provide an overview of the development of Freud's ground breaking discoveries regarding depression and identification in "Mourning and Melancholia", and how these ideas are reflected in our current psychoanalytic understanding of depression and of identification and its central role in the build-up of psychic structures.