The purposes of this chapter are (a) to situate current thinking on consciousness in the field of transpersonal psychology, (b) to formulate a distinction between states, levels, and stages of consciousness, and (c) to propose a heuristic model for the study of altered states of consciousness. Transpersonal psychology is concerned primarily with those aspects of human experience and behavior that lie beyond the personal, interpersonal, and social aspects studied in other psychological schools. Following Walsh and Vaughan (1980) in their distinction between transpersonal context, content, and process, I see the study of consciousness and its transformations as the central content area for transpersonal psychology.