This contribution highlights the ways in which UN Commissions of Inquiry apply the 1949 Geneva Conventions. This form of accountability for violations of the Geneva Conventions tends to be unseen, less well known than the work of Special Rapporteurs, Treaty Bodies, or War Crimes tribunals. Particular emphasis is placed on how a Commission can choose whether to describe an event as a violation of the Geneva Conventions or alternatively as a violations of a human rights treaty such as the Convention against Torture. There is also a discussion of violations of international law by non-state actors and how Commissions and other Special Procedures deal with this topic. Lastly, some of the principles that should guide access to the work of a Commission by national prosecutors and others are set out based on the experience of the UN Commission on HUman Rights in South Sudan.