Volume 2 of Cerebral Cortex continues our policy of dealing with the individual elements of the cerebral cortex before moving on in subsequent volumes to a consideration of the details of the various functional areas. Volume 1 of the treatise dealt with the morphology of cortical neurons, and Volume 2 continues this theme to some extent by including chapters devoted to the morphology of cortical neuroglial cells, of immunocytochemically labeled neurons, and of in­ tracellularly i~ected neurons. However, the major emphasis of this volume and of Volume 3, which will follow it, is on the functional characteristics of cortical neurons and neuroglial cells, particularly those of transmitter and receptor iden­ tity and of electrophysiological uniqueness. Volume 2 emphasizes these char­ acteristics in relation to the intrinsic cortical elements; Volume 3 will continue this and add chapters on the afferent and efferent systems of the cortex. Together, Volumes 2 and 3 will cover all of the transmitters, receptors, and related compounds that have so far been discovered in the cerebral cortex. It is the interrelations among the neuronal elements expressing these materials that determine the functional operations of the cerebral cortex, and the necessity for understanding how the appropriate cooperation between the neuronal ele­ ments is achieved is highlighted by Sir John C. Eccles's introductory chapter on "The Cerebral Neocortex: A Theory of Its Operation.