This special issue addresses the nature, development, and consequences of a variety of lay theories for group perception and behavior. The articles illuminate the structural, functional, and dynamic properties of lay theories, as well as their scope. Addressing the development of the theories from diverse theoretical perspectives-evolutionary, cognitive, developmental, and sociocultural learning-each paper documents the consequences of different lay theories for understanding group inferences and judgements. Collectively the articles propose theoretical extensions and suggest practical implications of the lay theories approach for reducing prejudice.