This book focuses on transnationalism as a key concept to evaluate how Europe experiences, perceives and responds to current cross-border security challenges from a legal and political perspective. The chapters in this volume specifically provide state-of-the-art accounts on several legal and political developments that have recently taken place in relation to transnational issues, such as terrorism, irregular migration and human rights violations. It specifically discusses how Europe experiences, perceives and responds to security challenges with the expectation to identify those facets of transnationalism that would ‘equally’ concern political scientists and legal scholars, especially those working on subjects pertaining to the EU governance. Through a timely analysis of the specificities of these cases, the book contributes to a much wider debate on whether and to what extent the changes and practices identified are still in accordance with cornerstones of the EU governance project, such as fundamental freedoms, democracy and the rule of law. Overall, the book provides a fresh reading on the current status of security across Europe and the way it is understood and practiced from a multidisciplinary perspective With a revised introduction and a new conclusion, this edited volume this is the ideal companion for students, researchers and practitioners interested in law, public policy and administration, and security. This book was originally published in the Journal of Contemporary European Studies.