In this book, Katarzyna Granat analyses and evaluates Europe's experience with the Early Warning System (EWS) which allows national parliaments to review draft legislative acts of the European Union for their compatibility with the subsidiarity principle. The EWS was introduced in response to the perceived 'democratic deficit' of the EU and its 'creeping' competences, and represented one of the landmark reforms of the Lisbon Treaty. The purpose of this book is to present and critically analyse the functioning of the new mechanism of subsidiarity review and the role that national parliaments have played within this system. Compared to the existing leading publications on the Europeanisation of national parliaments and contributions on the EU principle of subsidiarity, this book offers - for the first time - a profound legal analysis of the procedure enriched by a comprehensive empirical analysis of the activities of national parliaments. It is directed at scholars of EU law and policy, European and national officials, and legal practitioners working in and with the national legislatures.