Over the past two decades, mental retardation research converges on three general themes: co-occurring mental retardation and psychopathology; families of offspring with mental retardation; and the developmental approach regarding behavioral sequences and profiles. Intertwined with each theme is a mounting body of research on genetic mental retardation syndromes. We first review recent progress in each of the three domains--psychopathology, families, and development--based on studies of groups with heterogenous or nonspecific mental retardation. We then show how new findings from specific genetic syndromes take this knowledge even further, as well as aid in the search for genetic, physiological, and environmental mechanisms associated with certain behaviors. We end the review by briefly summarizing our reasons for promoting an etiological approach to future mental retardation research, as well as by discussing methodological and other challenges.