THE CONTRIBUTIONS OF 21 AUTHORS IN THIS VOLUME ARE DEVOTED TO ASSESSING THE STATUS OF RESEARCH AND THEORY IN MENTAL DEFICIENCY, FOCUSING ATTENTION ON THE BEHAVIOR OF THE MENTALLY HANDICAPPED. PART ONE IS CONCERNED WITH RESEARCH FINDINGS AND THEORIES TO EXPLAIN MENTAL DEFICIENCY. COMPREHENSIVE PSYCHOLOGICAL THEORIES REPRESENTED INCLUDE FIELD THEORY, A SOCIAL LEARNING APPROACH, THE HULL-SPENCE BEHAVIOR THEORY, AND THE SOCIAL PSYCHOLOGIES OF MENTAL DEFICIENCY. OTHER ARTICLES DISCUSS THE STIMULUS TRACE MECHANISM AND ITS EFFECT ON MEMORY, THE ROLE OF ATTENTION IN INTERPRETING EVIDENCE ON RETARDATE LEARNING, THE CONCEPT OF INTELLIGENCE AND ITS RELATION TO BRAIN DAMAGE, AND THE RELEVANCE OF GENETICS TO A CONSIDERATION OF HUMAN INTELLIGENCE. THE APPLICATION OF PIAGET'S THEORY TO MENTAL DEFICIENCY RESEARCH AND STUDIES IN THE SOVIET UNION ARE ALSO DISCUSSED. PART TWO PRESENTS EMPIRICAL FINDINGS CONCERNED WITH MENTAL DEFICIENCY. SEVERAL PAPERS DEAL WITH ASPECTS OF LEARNING--CLASSICAL CONDITIONING, PERCEPTUAL-MOTOR SKILLS, DISCRIMINATION, VERBAL PROBLEM SOLVING AND CONCEPTUAL BEHAVIOR, LANGUAGE AND COMMUNICATION, AND ACADEMIC SKILLS. THERE ARE ALSO DISCUSSIONS OF RESEARCH INVESTIGATING PSYCHOPHYSIOLOGICAL ASPECTS, SENSORY AND PERCEPTUAL PROCESSES, ACTIVITY LEVEL AND MOTOR SKILLS OF MENTAL DEFICIENCY. REFERENCES PROVIDED FOR CHAPTERS TOTAL APPROXIMATELY 1500. THIS DOCUMENT WAS PUBLISHED BY MCGRAW-HILL BOOK COMPANY, INC., NEW YORK, NEW YORK, AND IS AVAILABLE FOR $15.50. (UM)