Book excerpt: In this volume, the Gardners and their co-workers explore the continuity between human behavior and the rest of animal behavior and find no barriers to be broken, no chasms to be bridged, only unknown territory to be charted and fresh discoveries to be made. With the beginning of Project Washoe in 1966, sign language studies of chimpanzees opened up a new field of scientific inquiry by providing a new tool for looking at the nature of language and intelligence and the relation between human and nonhuman intelligence. Here, the pioneers in this field review the unique procedures that they developed and the extensive body of evidence accumulated over the years. This close look at what the chimpanzees have actually done and said under rigorous laboratory conditions is the best answer to the heated controversies that have been generated by this line of research among ethologists, psychologists, anthropologists, linguists, and philosophers.