This article discusses the development of the UNWCC and the intellectuals involved. It notes the commitment that smaller Allied states made to frame international criminal law with regard to war crimes. The article pays particular attention to two Czech delegates who stood out from the community of experts, and who were instrumental in formalizing how war crimes committed in Europe during the Second World War – and beyond – should be handled. The concept of crimes against humanity became a main outcome of the legal debates, serving not only as a blueprint for the London Charter, but the international criminal law system as a whole. The predecessors of the UNWCC, involving some of the most renowned lawyers of the time, formed one of the first truly transnational networks. Moreover, the experiences of the lawyers, and their framing of that experience in lengthy memorandums, helped to generate a new concept in politics: the protection of human rights.