Building and sustaining solidarity is a compelling challenge, especially in ethnically and religiously diverse societies. Recent research has concentrated on forces that trigger backlash and exclusion. This volume looks at the politics of diversity in the opposite direction, exploring the potential sources of support for an inclusive solidarity, in particular political sources of solidarity. We ask three questions: Is solidarity really necessary for successful modern societies? Is diversity really a threat to solidarity? And what types of political communities, political agents, and political institutions and policies help sustain solidarity in contexts of diversity? To answer these questions, the volume brings together leading scholars in both normative political theory and empirical social science. Drawing on in-depth case studies, historical and comparative research, and quantitative cross-national studies, the research suggests that solidarity does not emerge spontaneously or naturally from economic and social processes but is inherently built or eroded though political action. The politics that builds inclusive solidarity may be conflictual in the first instance, but the resulting solidarity is sustained over time when it becomes incorporated into collective (typically national) identities and narratives, when it is reinforced on a recurring basis by political agents, and—most importantly—when it becomes embedded in political institutions and policy regimes. While some of the traditional political sources of solidarity are being challenged or weakened in an era of increased globalization and mobility, the authors explore the potential for new political narratives, coalitions, and policy regimes to sustain inclusive solidarity.