This report presents results from three research studies that were designed to explore both the definition and the structure of the adaptive behavior construct. The first study investigated the structure of adaptive behavior as a function of age, developmental level, and type of handicap through an exploratory factor analysis of both the individual items and the subscales of the "Scales of Independent Behavior." Samples for the study consisted of 1,958 nonretarded individuals from preschool-age to adults, and 288 retarded individuals, aged 76 months to adults. The second study sought to extend a prior review of adaptive behavior factor analytic research through analysis of nine new studies and re-examination of seven sources. The third study explored the relationship between adaptive behavior, maladaptive behavior, and intellectual/academic ability through the application of multivariate statistical methodology with subjects from the first study and 556 additional children in grades 1-8. Results of the three studies showed that adaptive behavior, maladaptive behavior, and intellectual/academic ability represent related but different constructs. Current psychoeducational assessment practices provide good coverage of conceptual intelligence, practical intelligence, and social/emotional adaptation, but are weak in the coverage of social intelligence. (JDD)