Expecting a gentle baby tiger to inevitably grow up to be ferocious, a young girl growing up in a household of boys to prefer princesses to toy trucks, or that liberals and conservatives are fundamentally different kinds of people, all reflect a conceptual commitment to psychological essentialism. Psychological essentialism is a pervasive conceptual bias to think that some everyday categories reflect the real, underlying, natural structure of the world. Whereas essentialist thought can sometimes be useful, it is often problematic, particularly when people rely on essentialist thinking to understand groups of people, including those based on gender, race, ethnicity, or religion. This Volume will bring together diverse theoretical and methodological perspectives on how essentialist thinking about the social world develops in childhood and on the implications of these beliefs for childrens social behavior and intergroup relations more generally.