The history of the concept of splitting and the multiple references it has accumulated are discussed. I then trace the development of the splitting process as an initial form of upper-level organizing functions which emerge in an evolving hierarchy of ego capacities. The roles such a process plays in later versions of both the synthetic function proper and the evolving defensive repertoire are delimited. In a discussion of clinical material from borderline and psychotic pathologies, I consider the role splitting plays in the ego's relations as an agency to the systems of mental content (e.g., the self) it helps elaborate. In this manner I attempt to account for perceivable differences in the "depth" and character of the splitting manifested by each pathology. The question of availability to consciousness is raised in order to examine the developmental, structural, and energic relations between splitting and repression and to preface a discussion of the organizing and defensive roles splitting may play in later normal development.