Subsidiarity and Solidarity within the European Union:A Double-Edged Sword

Subsidiarity is often portrayed as a solidarity-promoting principle in the European Union because it promises that authority is exercised at the most appropriate level. This chapter argues, however, that subsidiarity is a double-edged sword for EU solidarity because it operates as a contested norm within a broader competence regime that structures how authority is allocated, justified, and challenged. We trace subsidiarity’s historical development and show how its conceptual flexibility makes it a strategic resource that can legitimate both centralization and decentralization. We then examine the Lisbon Treaty’s early warning system, focusing on the yellow card procedure, to show how subsidiarity review institutionalizes contestation but rarely constrains the Commission decisively, even when proposals touch solidaristic concerns. Turning to Social Europe, we argue that subsidiarity functions as a strong presumption for national competence that channels solidarity toward backstopping, coordination, and re-insurance rather than enforceable EU-level social rights. Finally, we show that in major crises subsidiarity becomes politically secondary as emergency logics and executive bargaining dominate, even as solidarity becomes indispensable for mobilizing resources and sustaining collective action.