This thesis examines the application and interplay of international humanitarian law (IHL) and human rights law (HRL) during peace operations. For the interaction of the different substantive provisions under both legal regimes, the thesis’ focus is specifically on the circumstances and modalities under which physical force may be used against individuals. As for the application of IHL, the ordinary threshold requirements (i.e. on intensity) constitute the primary tool for examining whether a peace operation has become a party to an armed conflict. This thesis, however, suggests an additional participation-based test for situations where the peace operation directly supports a party to a pre-existing armed conflict in the mission area. IHL continues to apply – without strict spatial limitation – until the overall armed conflict comes to an end or the peace operation ceases its hostile acts and support. The application of HRL in the mission area is, as this thesis argues, subject to a gradual test: negative obligations need to be observed at all times, while the application of positive HRL obligations is contextspecific (e.g. degree of control). In addition, the thesis offers different models to overcome the legal challenges in relation to extra-territorial derogations and shows how the procedural requirements and additional safeguards may operate in the context of a peace mission. As a consequence, IHL and HRL often apply to the same situation in the field – both in time and space. This leads to a potential conflict between the different sets of use-of-force rules applicable to peace operations. In a nutshell: while HRL only allows for killings in response to threats to life and limb, IHL provides for lethal targeting based on status and conduct (even absent such threats), but contains stricter rules on the use of specific weapons and methods. Neither the individual scopes of application, nor the traditional interaction models (i.e. lex specialis and most-favourable-protection principle) are able to overcome this norm conflict. That is why this thesis suggests a model based on a distinction between two mutually exclusive paradigms: (1) the paradigm of hostilities involving active combat and governed by IHL, and (2) the paradigm of law-enforcement, which covers all remaining situations and is based on ordinary HRL standards. Usually, the IHL categories of the person in question (i.e. combatants vs. civilians) may give a first indication as to which paradigm applies. However, even for persons generally targetable under IHL, the use of force against them shifts towards the law-enforcement paradigm once the area in question is under the firm control of the peace operation or its allies. In addition, the specific IHL rules on certain weapons and methods provide for a sufficiently broad law-enforcement exception. This makes it even more necessary for commanders to provide careful planning and real-time instructions in order to fully operationalise the suggested distinction between the two paradigms.