The branch of clinical psychology known as behavior modification or, synonymously, applied behavior analysis, has grown substantially from humble beginnings in the 1960s. Many colleges and universities now offer courses in applied behavior analysis, and more than a few grant degrees in the area. Although they remain controversial, behavior mod- ification procedures have been used to good advantage in dealing with a range of problem behaviors and are now rather widely employed in schools, residential institutions, and other therapeutic facilities. The two hallmarks of applied behavior analysis...