This policy brief reviews the legal questions associated with the participation of civilians in hostilities. This issue represents a critical challenge to the protection of civilians in current conflicts, particularly when hostilities are conducted in the midst of civilian populations and assets, and when non-state armed groups are engaged as central actors. This issue is also of particular relevance when the hostilities occur under occupation. While international law recognizes a basic right of selfdetermination for populations under occupation, it provides immunity against violence only to those not participating in hostilities. This apparent contradiction is at the core of the debate on the protection of civilians and raises a number of questions about the roles and rights of civilians in armed conflict, as well as the concept of participation in the war effort and the nature of hostilities. Is a member of a militant group necessarily a “combatant”? Can he or she be targeted according to the rules of international humanitarian law (IHL)? Is membership the key criterion, or are the actual acts of the individual the deciding factors of his or her status under the law? How can a civilian maintain or restore his or her protected status? Practitioners face these and related questions when developing policies for civilian protection in the occupied Palestinian territory (OPT). As with all briefs in this series, this paper focuses on providing practitioners with a clear understanding of the legal framework available for protecting Palestinian civilians living in the OPT, as well as the legal regime applicable to both the Israeli military and Palestinian militants when they engage in military operations. This framework is based on IHL (and, in a broader sense, on international human rights law). This note explores the spectrum of opinion (amongst both scholars and practitioners) on the question of the legal implications of civilian participation in hostilities, in particular the legality of targeting civilians who engage in hostilities. It highlights debates ongoing in the field of IHL without attempting to present “correct” answers, with an eye to enhancing practitioners’ understanding of the types of legal rationale used both to limit and allow targeting of civilians who engage in hostilities. Ultimately, the aim of this brief is to strengthen the capacity of professionals to utilize and negotiate with the law while developing strategies to enhance the protection of civilians.