Identified Neurons and Behavior of Arthropods presents for the larger audience the papers delivered at a symposium of the same title. I organized this symposium so that a few of the many who owe him a great scientific debt could honor Professor C. A. G. (Kees) Wiersma upon his attaining the age of 70 and retiring from the California Institute of Technology. Everyone of the participants publicly acknowledged his debt to Kees Wiersma, but in a sense there was no need to do so, because the research reported spoke for itself. Seldom in a rapidly developing branch of modem science has all of the recent progress so clearly stemmed from the pioneering work of a single figure. But in this subject, the role of identified nerve cells in determining behavior, Wiersma stood virtually alone for 30 years. He it was who first showed that individual nerve cells are recognizable and functionally important and have "per­ sonalities" of their own.