Intergroup bias is a pernicious phenomenon in human societies. Its ubiquity led many theorists to argue that it is an inevitable result of inherent properties of human psychology. One such property is the tendency to essentialize social groups. A productive approach to assess whether any property of human psychology is indeed inherent is to trace its developmental origins. In this chapter, I review the current evidence on the development of social essentialism. One conclusion from this review is that by age 5, children around the world essentialize social categories. A further conclusion is that there is between- and within-cultural variation in who essentializes and who is essentialized. In other words, group identity is crucial for understanding the phenomenon. I discuss the factors—cultural and motivational—that possibilitate these variations. I end by tracing future directions for research to pursue and further elucidate the origins of—and ways to remedy—this potentially malign conceptualization of people.