This chapter provides a critical assessment of the enforcement system of international humanitarian law (IHL), also referred to as the law of armed conflict (LOAC) or jus in bello. The notion of enforcement should be distinguished from that of implementation, which is much broader, in that enforcement involves at least some degree of sanctioning for violations of IHL, which could encompass individual criminal responsibility or State responsibility and liability for reparations. After briefly discussing several factors that induce compliance with IHL, this chapter focuses on IHL enforcement at the three possible levels. At the domestic level, the chapter starts from the obligations imposed on States under the 1949 Geneva Conventions (GCs) and their two Additional Protocols of 1977 (AP1 and AP2), including the obligation to investigate and prosecute war crimes amounting to grave breaches. At the regional level, the chapter addresses the enforcement of IHL through the regional human rights systems, focusing on the three regional human rights courts, but also including relevant findings by the Inter-American Commission on Human Rights and the African Commission on Human and Peoples’ Rights. At the international level, the chapter analyzes the enforcement of IHL by discussing briefly the mechanisms included under IHL treaties, including Protecting Powers, the ad hoc and the standing International Fact-Finding Commission (established through Article 90 of AP1), and the ICRC. The focus then shifts onto the main UN organs, including the Security Council, the General Assembly (and its subsidiary bodies, the Human Rights Council and the International Law Commission), and the International Court of Justice (ICJ). Another type of enforcement mechanisms addressed here includes international criminal courts and tribunals. Finally, the chapter addresses briefly the role of non-State actors, focusing on non-State armed groups (NSAGs) and nongovernmental organizations (NGOs).