‘Psychological essentialism’ is the belief that members of a category share deep-seated properties that determine their identity. In the case of social categories, such beliefs have a variety of important implications. We review recent research that shows a central role for essentialist thinking in stereotyping, prejudice, and discrimination. Special attention is paid to beliefs about race and ethnicity, gender, sexual orientation, mental disorder, and personality. Lingering questions about essentialist thinking are discussed, and several directions for future research are suggested.