Unions and unionisms are important because they offer an alternative form of politics to that of nation-states and nationalisms. They allow a wider variety of relations between a plurality of peoples, opening prospects of resolving territorial politics. But unionisms, as state- or polity-centred perspectives, are also typically power-centred, often using the resources of the polity to resist assertion by their members, thereby turning democratic challenges into secessionist ones. Unionisms in Times of Change: Brexit, Britain and the Balkans focusses on these two faces of unionisms: the flexible alternative to the nation state, and the assertor of central power. This book is particularly timely at a period when the unions of the British Isles and of Europe have been disrupted by the process of British exit from the European Union, creating new dilemmas and options for unionisms in Northern Ireland. The chapters in this volume map the conceptual structure of unionisms; the ways unions are defined and defended in Northern Ireland, the United Kingdom, the European Union, the Balkans and Moldova; the ways they deal with challenge, conflict and change; the prospects of negotiation; the ways unionisms move from flexibility and accommodation to repression and back; and the opportunities for agreement and conflict resolution. The chapters in this book were originally published as a special issue of the Irish Political Studies.