The 'protection of civilians' mandate in United Nations (UN) peacekeeping operations fulfils a critical role in realising broader protection objectives, which have in recent years become an important focus of international relations and international law. The concepts of the 'protection of civilians' constructed by the humanitarian, human rights and peacekeeping communities have evolved somewhat separately, resulting in disparate understandings of the associated normative bases, substance and responsibilities. If UN peacekeepers are to effectively provide physical protection to civilians under threat of violence, it is necessary to untangle this conceptual and normative confusion. The practical expectations of the use of force to protect civilians must be clear, and an overarching framework is needed to facilitate the spectrum of actors working in a complementary way towards the common objectives of the broader protection agenda. Keywords: protection of civilians, peacekeeping, United Nations, international humanitarian law, international human rights law, responsibility to protect.