This book addresses the question of political legitimacy in the European Union from the much neglected angle of political responsibility. It develops an original communitarian approach to legitimacy based on Alasdair MacIntyre's ethics of virtues and practices, that can be contrasted with prevalent liberal-egalitarian and neo-republican approaches. Tsakatika argues that a 'responsibility deficit', quite distinct from the often discussed 'democratic deficit', can be diagnosed in the European Union. This is documented in chapters that provide in-depth analysis of accountability, transparency and the difficulties associated with identifying responsibility in European governance. Closing this gap requires going beyond institutional engineering. It calls for gradual convergence towards certain core social and political practices and for the flourishing of the virtues of political responsibility in Europe's nascent political community. Throughout the book, normative political theory is brought to bear on concrete dilemmas of institutional choice faced by the EU during the recent constitutional debates. *Political responsibility and the European Union* will be of interest to specialists and postgraduate students of political theory, constitutional law and European Union Studies.