A security measure designed to neutralize threats from an enemy party, internment is common in warfare. In the context of internment operations in Afghanistan, Iraq, Guantanamo Bay and the Democratic Republic of the Congo, and of increasing international military intervention in internal conflicts more generally, the legal framework for internment has been widely criticised for being at best ambiguous and full of loopholes, at worst out-dated and inadequate.In light of such criticism, this book examines the continued relevance and adequacy of the existing legal framework, identifies its shortcomings and proposes possible avenues to remedy them. It offers answer to fundamental questions such as who may be lawfully interned in armed conflict, on what legal basis, for what reasons and for how long. She lays bare significant challenges in non-international armed conflict, such as the lack of a legal basis to intern in international humanitarian law and the serious risks involved in solutions proposed so far to remedy that gap. Indeed, sole reliance on international human rights law, domestic law or, alternatively, on the rules on targeting are unsatisfactory and inappropriate. Heeding calls for the clarification and modernization of the existing legal framework for internment in armed conflict, the author puts forward concrete proposals for normative developments that seek to reconcile both the practical realities of contemporary armed conflict and significant developments in international law that affirm the right to liberty as one of the most fundamental attributes of any human being.