Can populism be a source of long-lasting changes in citizens' beliefs, behaviors, and political identities? This chapter follows recent literature in treating populism as identity-shaping. Populist movements mobilize constituencies based on anti-establishment appeals that draw a wedge between a "corrupt elite" and a "victimized people" of the nation. It is electorally advantageous to define the "people" in a broad but bounded way, such that there is simultaneously a large, heterogeneous coalition of voters and a clearly defined enemy. We show through observational and experimental evidence that populism's emphasis on a broad but bounded concept of the people can shape the distribution of citizens' identities by reducing the cost and increasing the benefit of assuming non-elite social identities. Populist discourse is thus an identity-shaping political tool that can serve to incorporate those at the margins. This heterogeneity, however, creates a sustainability problem. With little to glue its members together beyond their anti-elite status, populist support coalitions are particularly vulnerable to disintegration after victory. We argue that some correlates of populism, like redistributional economic policies, and a tendency to organize constituents, are driven by the populists' need to stabilize their support coalitions. We argue that these are identity-stabilizing political tools.