For centuries, since the Roman Empire's adoption of Christianity, the continent of Europe has been perceived as something of a Christian fortress. Today, the increase in the number of Muslims living in Europe and the prominence of Islamic belief pose questions not only for Europe's religious traditions but also for its constitutional make up. This book examines these challenges within the legal and political framework of Europe. The volume's contributors range from academics at leading universities to former judges and politicians. Its 19 chapters focus on constitutional challenges, human rights with a focus on religious freedom, and securitisation and Islamophobia, while adopting supranational and comparative approaches. This book will appeal not merely to academics and law students in the UK and the EU, but to anyone involved in diplomacy and international relations, including political scientists, lobbyists and members of NGOs. It explores these contested relationships to open up new spaces in how we think about religious freedom and co-existence in Europe and the crucial role that Islam has had, and continues to have, in its development.