This volume arose from a desire to advance academic discourse and reflection on the broader subject of prolonged occupation, in light of the permanent character, and resulting implications of, the 55 year Israeli administration of the Palestinian Territories. The roots of the volume lie in a 2018 academic conference on "The Threshold from Occupation to Annexation". The present volume moves that discussion forward, updating and widening the range of topics addressed. The result is a collection of thought-provoking contributions by a wide range of scholars on the challenging and critical issue of prolonged occupation and international law, ranging from colonialism, apartheid, the illegality of occupation and potential international criminal liability.