This monograph is based on 20 years of research with patients who have experienced pathology in one hemisphere of the brain. It deals with brain mechanisms in human communicative behavior, and with related motor functions, from a broadly biological point of view. In so doing, the workdiscusses the possible evolutionary origins of human communication, the relation of brain mechanisms in communicative behavior to analogous nonhuman behaviors, and the neural systems involved in various levels and kinds of communication. In addition, noncommunicative mechanisms which parallel thoseused in communication--such as manual and oral praxis, and constructional behavior-- are outlined in detail. Individual differences in brain organization for such functions, related to hand preference and sex, are also explored. Although there is extensive reference to central nervous systempathology, the emphasis throughout is on how the findings contribute to understanding normal brain mechanisms. Much new data is presented along with the theoretical treatment of human communication which emphasizes a behavioral rather than a linguistic approach. This in turn provides continuitywith nonhuman primates and early hominids. The work will interest psycholinguists, cognitive psychologists, neurologists, clinical neuropsychologists, speech pathologists, and advanced students in these fields.