The law of armed conflict (LOAC) emanates from the same legal sources as general public international law. Accordingly, LOAC is found primarily in treaties and customary international law, in addition to general principles of law, legally binding unilateral acts and legally binding resolutions of intergovernmental organisations. Furthermore, judicial decisions and international legal scholarship constitute subsidiary sources. These sources and their idiosyncratic features in the context of LOAC are addressed in turn. The subsequent section addresses LOAC rules as norms of jus cogens and as erga omnes obligations. The chapter then turns to an examination of the Martens Clause and its legal significance, followed by a section that examines the situation in which several states with different legal obligations interact and operate jointly, before some concluding remarks are offered.