For almost two hundred years the problem of localization of the brain processes has been provoking discussion in the fields of medicine, philosophy, and in general critical reflection that at times is expressed in acute polemic terms—phrenology, the disputes over aphasia between 1861 and 1865, the Bergsonian interpretation of P. Marie's works, and so on—and at times dies down and seems to disappear. In the past quarter of a century, this discussion has not lost any of its fascination, but it cannot possibly be tackled without at least a minimum of historical background. We therefore propose, first of all, to review the main elements highlighting the development of the problem, since its present state becomes meaningful only in relation to the recent past. Since we cannot permit ourselves to recapitulate all aspects of its history in the course of this article, we shall give examples in the four fields we feel to be the most pertinent: human and animal neuropsychology, neurophysiology and neurochemistry. Finally, we shall set forth our reflections on the heuristic meaning of these examples, and endeavor to draw conclusions, some of which may answer problems that have never been raised before.