This chapter examines the legal norms governing investigations of possible international law violations during an armed conflict. It begins by setting forth those rules derived from the 1949 Geneva Conventions, 1977 Additional Protocols and customary law. Since human rights norms also apply in armed conflicts, the chapter surveys human rights investigatory standards, and how they interact with corresponding international humanitarian law rules. Since international humanitarian and human rights law on the subject lacks granularity, State practice is surveyed in order to tease out prevailing practices that may either reflect on how treaty law is applied or reveal the broad outlines of customary law. The chapter offers conclusions as to the applicable legal standards for such investigations.