Increasing knowledge of human cerebral hemispheric specialization suggests a relationship between the different formal modes of thinking attributed to the two hemispheres and those psychoanalysis has traditionally assigned to primary (similar to recessive hemispheric) and secondary (similar to dominant hemispheric) processes. The fact of a lifelong capability at the neurophysiological level for coequal, simultaneous registration and organization of experience in these different cognitive modes allows primary process to be conceptualized in developmental terms. As the first organizing mode of infantile development, it shapes the primitive content of the dynamic unconscious. Thereafter, it can be viewed as coexistent and commingled with secondary process in dynamic tension, complementarity, and developing complexity. Observations from normal behavior, current research, and the functioning of the psychoanalyst support this thesis and reinforce an emerging viewpoint in contemporary psychoanalysis that primary processes are not confined to archaic levels but are open to growth and developmental integration into the complete range of ego functions.