This chapter explores the complex ethical challenges of researching war crimes, using my research on sexual violence in the conflict in the former Yugoslavia as a case study. The chapter explores three key sets of ethical challenges in this area. The first concerns how the researcher defines war crimes, as this includes or excludes forms of conduct, and accordingly, categories of victims and perpetrators. The second set of ethical challenges arises from the context of conflict, which situates the researcher in an acutely violent and politicized research field. The third set of challenges relate to the choice of methodology and methods, which is integral to research quality and integrity in this difficult field. The chapter examines each of these ethical challenges through the practice of researching war crimes in the field. It connects practical ethics issues, such as confidentiality, to the broader ethical questions of the values and principles of research, such as social justice commitments, that this area inevitably raises.