Detention and occupation are two challenging aspects of international humanitarian law in 21st century warfare. The essays selected for this volume examine the historical foundations of these issues, as well as the contemporary practices surrounding them. Detention law was prominently codified in the 1949 Third and Fourth Geneva Conventions, but has been criticized as inadequate in the face of 'new wars' involving non-State actors such as insurgents and terrorists. These essays not only explore historically problematic detention issues like repatriation and the protecting powers regime, but also question whether the extant law suffices to ensure a proper balance between humanitarian considerations and a detaining State's security concerns. Occupation law was originally designed for temporary occupations that maintained the occupied State's institutions pending return of full authority, but has been tested by recent occupations which are often prolonged and which sometimes seek to 'transform' occupied States previously governed by undemocratic and abusive regimes. The essays demonstrate that these are not novel issues and consider how they were handled in the past. They also assess various perspectives as to the purposes and limits of occupation, especially in the face of modern imperatives such as human rights.