This chapter discusses the conceptual, principle, and technological basis for the behavior modification approach to adaptive problems presented by the mentally retarded. It presents data relative to applications of this approach to the mildly, moderately, severely, and profoundly retarded. The chapter provides a review of applications to the mildly and moderately retarded in school and occupational and social adjustment training settings. Positive teaching approach requires that we know about what the retarded can do in a variety of behavior areas. The student's behavioral limitations should be translated into present behavioral characteristics. A great deal of valuable information is obtainable only through observation of the person in various structured and unstructured and in work and play settings. Recognition of the crucial role which this law of reinforcement assumes in the learning of the retarded suggests a consideration of those environmental events which are reinforcing.