In this chapter, we address the relationship between crowd events and the social categories that organise our everyday lives. According to conventional wisdom, crowd events are a pathological disruption of everyday life caused by either a loss of individual identity or a congregation of individuals with pathological identities. We examine and critique this approach before going on to explore the various ways in which crowd events create and endorse social identities (group memberships) within the wider population of non-participants in society. In other words, if you want to understand social identities and social relations in society - both what they are and how they are produced - look to the crowd. Crowds constitute the social imaginary: they both reflect and shape the way we think about the groups to which we belong and our relations with others. The idea that crowds play a critical role in the construction of the social imaginary for both those who participate in crowds and those who observe them directly or through the media is controversial because it counters traditional wisdom, and at the root of this argument is a very specific understanding of social identities and their political significance.