This book is a ground-breaking study of how the European Court of Human Rights interprets Article 5 of the European Convention on Human Rights - the right to liberty and security. The right to liberty is a fundamental provision that is enshrined not only in the Convention but in all major human rights treaties. Despite this, Article 5 remains both a largely underdeveloped and unexplored area of European human rights law. The work aims to fill this gap by presenting an original framework for the progressive interpretation of the right to liberty. It is argued that the Court has not made use of opportunities to evolve Article 5 standards, resulting in a weakening of protections against arbitrary detention. This book's original framework for the progressive interpretation of Article 5 identifies and addresses gaps in the protection of vulnerable groups of detainees, including in areas of growing concern across the European human rights space. These include individuals held pre-trial, as children, in immigration detention, following protest, or as a result of their political dissent or human rights activism. The volume outlines the normative justifications for an evolutive approach to Article 5 and elaborates how a dynamic interpretation could be enacted in practice, including by reference to original interview data and insights from European Court of Human Rights judges. This book will serve as a key point of reference for anyone researching or working on detention and the right to liberty across the Council of Europe and beyond. The Open Access version of this book, available at http://www.taylorfrancis.com, has been made available under a Creative Commons Attribution (CC BY) 4.0 license