Sidney W. Bijou is Professor of Psychology and Director of the Child Behavior Laboratory at the University of Illinois, Urbana-Champaign. A PhD of the University of Iowa, Bijou taught at the University of Washington during 1948-65. He has made many contributions to the literature in child development and behavior modification. His books include two coauthored with D. M. Baer, Child Development: A Systematic and Empirical Theory, Vol. 1, and Child Development: The Universal Stage of Infancy, Vol. 2. Emilio RibesInesta, the second editor, is Professor of Psychology at the National Autonomous University of Mexico in Mexico City. He has played a key role in introducing behavior modification to Mexico. RibesInesta is coauthor (with F. S. Keller) of Behavior Modification: Application to Education (in press). Reviewer Gerald C. Davison, a PhD of Stanford University, is Professor of Psychology and Director of the Postdoctoral Program in Behavior Modification, State University of New York at Stony Brook, whose faculty he joined in 1966. During 1969-70, he was Visiting Professor at Stanford. Davison has published widely in behavior therapy and related areas and is President (1973–74) of the Association for Advancement of Behavior Therapy. He is coauthor of Abnormal Psychology: An Experimental Clinical Approach, and coeditor of Contemporary Readings in Psychopathology.