Researchers and practitioners alike have long focused on the external life conditions, adaptive behavior, and inclusion of persons with mental retardation. Using breakthroughs in positive psychology, this article proposes a new research agenda focused on the positive, internal states of those with mental retardation. It shows how major movements in the mental retardation field—quality of life, dual diagnosis, personality motivation, and families—have succeeded in some arenas but failed to address happiness and well-being. Examples of happiness—of positive emotions, flow, strengths, and virtues—are offered in people with genetic causes of mental retardation. Complexities related to etiology, measurement, flow, and a meaningful life are described, as is the vital role that mental retardation can play in the emerging science of positive psychology.