The nature of security in Europe has been transformed in recent years. Security in 21st Century Europe argues that the defining feature of contemporary European security is the existence of a security community underpinned by the twin institutions of the EU and NATO, but that today the European security community, NATO and the EU face a growing array of external challenges and their ability to respond to those challenges is increasingly being called into question. Offering a systematic assessment of security in contemporary Europe, this third edition examines the changing character of European security and assesses the extent of the threats posed by recent challenges, as well as the policy dilemmas involved in responding to these challenges. It explores Europe's engagement with core thematic issues in European security, including military intervention, nuclear weapons, terrorism and non-military security. Providing both a substantive contribution to academic thinking on European security and a overview of debates on contemporary European security, this new edition offers: - Three new chapters on migration, climate change and cybersecurity - Coverage of all recent major developments related to European security, including: the Syrian civil war and the regional destabilization arising from it; Russia-Ukraine crisis; the rise of populism; the migration crisis; the acceleration of China's rise. Security in 21st Century Europe combines theory and detailed empirical analysis, exploring both how different theoretical perspectives can help us think about European security and concrete empirical developments in European security policies and institutions. This text is the perfect companion for advanced undergraduate and Master's level courses on European security, whether within courses in Security studies, European studies or International Relations.