»International Humanitarian Law and Non-State Actors. NGOs and the Tension between Necessary Cooperation with Armed Non-State Actors and Public Security Interests«: Compliance with international humanitarian law by armed non-state actors is critical for the protection of civilians in non-international armed conflicts. A detailed analysis shows that NGOs can at times reach out to armed non-state actors more easily and engage them to respect the law. Despite this necessity of cooperation, NGOs increasingly encounter obstacles due to public security interests and counter-terrorism legislation.