Demonstrating how race is socially constructed has been a core sociological objective, yet many individuals continue to hold essentialist and other concepts of what races are and how to account for group differences. These conceptualizations have crucial consequences for intergroup attitudes, support for social policies, and structures of inequality, all of which are key sociological concerns; yet much of the research in this area has emerged outside of sociology. Our review of this interdisciplinary scholarship describes the range of views people hold, the attitudes and behaviors associated with them, and what factors contribute to these views. We focus primarily on essentialism and constructivism, although we describe the greater variety of beliefs beyond this dichotomy, as well as fluidity in how people use these concepts. We conclude by presenting research on strategies for reducing essentialist belief systems and identifying key areas for future research. Expected final online publication date for the Annual Review of Sociology, Volume 49 is July 2023. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.