InJuly 1982 the first Dartmouth workshop on the corpus callosum took place. A nucleus of basic and clinical scientists was convened to give progress reports of their work on the corpus callosum. This text was subsequently compiled by the various participants from these reports modified by a stimulating cross fertilization of ideas and subsequent studies. Four and one-half decades have intervened since Van Wagenen first sectioned the corpus callosum for epilepsy (Van Wagenen and Herren, 1940) and Erickson (1940) demonstrated that the corpus callosum is the major route for generalization of experimentally induced focal cortical epilepsy. During the succeeding 45 years a handful of clinicians has pursued these leads to confirm the therapeutic value of callosotomy for some types of medically intractable generalized epilepsy. Parallel experimental studies with a number of epilepsy models have indicated that the corpus callosum is indeed the major route for seizure generalization, that the brainstem is a secondary and more resistant pathway for seizure generalization, and that most if not all epileptic seizures originate from the cerbral cortex. The unexpected clinical finding that even partial (focal) seizure incidence is modified by callosotomy now has been demonstrated in the laboratory. The various contributors to the clinical and experimental epilepsy sections of this volume have been seminal in these elucidations, as will be evident from their chapters. The section on the development, anatomy, and physiology of the corpus callosum demonstrates that these basic areas of study have not been neglected.