In this chapter forthcoming in Ben Saul (ed), Research Handbook on International Law and Terrorism, I consider the compatibility of counter-terrorist detention with international human rights law from the starting point that what is protected in international law is not a right to be free from detention per se but rather a right to be free from the arbitrary deprivation of one’s liberty. This is clearly rooted in international human rights law, which is the main focus of this chapter (acknowledging that it interacts with international humanitarian law in situations of armed conflict). The chapter demonstrates that counter-terrorist detention can be compatible with the standards of international human rights law as they have been interpreted and applied in the past decade, but that in the process of such interpretation and application those standards have at times been diluted to a worrying extent.