This booklet, together with the following two,-which are well under way and will succeed it at intervals of, we hope, no more than six months, sets the stage for a new editorial enterprise in the field of brain science. The accent is on the functional aspects of brains rather than on their develop- ment, hence the title of the series. The central question being how neural activity is related to behavior, there will be, naturally, a wide scatter of sub- jects, and Heiligenberg's monograph on electric fish may be considered typ- ical of the expected standard deviation from the mean. Deviations in other directions may go as far as the sensory neuron, or brain theory, or aphasia, or farther. The next contributions planned for the series are: Precht, Neuronal Operations in the Vestibular System, and Movshon, Genes and Environment in the Development of the Visual Cortex. Our aim is to ap- proach the central area by means of something like an evolving handbook of brain science. The individual monographs should describe promising and successful approaches, even in areas where the last word is far from being said. Besides originaI monographs and compounds of the author's own published papers, reviews are also we1come if they are more than the sum of the parts. The publisher promises speedy publication, and the editors will see that the manuscripts will be readable as well as interesting. Tubingen, Summer 1977 V.