The multifaceted nature of peace operations today and the increasingly violent environments in which their personnel operate increase the likelihood of their being called upon to use force. It thus becomes all the more important to understand when and how international humanitarian law (IHL) applies to their action. This article attempts to clarify the conditions for IHL applicability to multinational forces, the extent to which this body of law applies to peace operations, the determination of the parties to a conflict involving a multinational peace operation and the classification of such conflict. Finally, it tackles the important question of the personal, temporal and geographical scope of IHL in peace operations.

This article describes some of the challenges raised by multinational operations for the application of international humanitarian law. Such challenges are the result of different levels of ratification of treaties, divergent interpretations of shared obligations, and the fact that there is no central authority that determines who is a party to an armed conflict. The article discusses methods that have been developed to ensure ‘legal interoperability’. Some of these methods attempt to avoid situations where such interoperability is required. Where this is not possible, a ‘maximalist’ or a ‘minimalist’ approach can be taken, and in practice these are usually combined.