Social essentialism consists of the commonly held belief that certain ways of categorizing people (e.g., gender and race) reflect meaningful, fundamental distinctions found in nature—that some kind of category “essence” (e.g., something in their blood or their DNA) explains why groups of people (such as boys and girls) are different from one another. Yet as common as they are, essentialist beliefs can give rise to adverse consequences, including stereotyping and social prejudice. In this chapter, we examine the development of social essentialism. To begin, we briefly address the evidence that these beliefs are the result of developmental processes that unfold beginning in early childhood (and not something innate that children are born with). Then, we consider the nature of those processes; specifically, how basic processes underlying conceptual development give rise to different components of essentialist beliefs. We then address how different essentialist beliefs might be integrated into a coherent essentialist view of a category, and finally into a coherent essentialist view of a domain.