This article introduces a special issue of West European Politics on the COVID-19 crisis. It first sets out the dual challenge to democratic principles and democratic performance that the COVID-19 pandemic has posed to European liberal democracies. Three bodies of scholarship are especially relevant in framing this dual democratic challenge: those that provide accounts of policy, institutional and legitimacy crises; accounts of the governance of emergencies and of emergency politics; and accounts of political turbulence and organisational and policy responses. The articles that comprise the special issue provide comparative empirical insights into first reactions, with a focus on the responses by political decision-makers, European publics and the EU. Assessments of the likely longer-term, potentially transformative effects of COVID-19 on the principles and performance of European liberal democracies will need to draw on both sectoral and systemic perspectives, with a focus on the organisation and operation of public authority and the state. KEYWORDS COVID-19; liberal democracy; crisis; emergency; turbulence; state COVID-19, which began to appear on the political agenda of European democracies at the start of 2020, has constituted a singular political challenge. It has involved every level of government, from the local to the global, and all branches of government, including executives, parliaments and courts. It has affected all citizens. It has touched every sphere of life, from the public through to the private. It has extended to virtually every policy domain. Its political effects have been rapid, pervasive and profound.The COVID-19 crisis has challenged public policy making, with public health policy at the core, but very quickly diffusing through to many other policy domains. It has put to the test the reactive and adaptive capacities of governments, administrations, specialised agencies, legislatures and courts, notably, but not exclusively, administrative and constitutional