The ways in which an individual (the subject) relates to and perceives other people (his or her "objects") has been a preoccupation of psychoanalysis and in recent years a plethora of concepts has grown up in the literature. In this study, the changing meanings of the different concepts are explained from context to context, discussing in depth the theoretical issues underlying them. The text includes an historical survey of how mental objects have been understood in the various "schools" of psychoanalysis as they have developed. The topics discussed include: Freud and his associates; the object-relations approaches of Klein, Fairbairn and Bion; orientations derived from ego psychology such as those of Schafer and Kernberg and the self orientation of Winnicott and Kohut. The author also discusses the conceptual and clinical issues involved in the major differences between the concepts. The three basic meanings of the concepts of mental objects as they have emerged in the literature are demonstrated showing how they are related to ongoing issues in contemporary psychoanalysis.