Hong Kong's war crimes process, adjudicating offences from Hong Kong and the New Territories, China (Taiwan, and also Shanghai and Waichow), Japan, and on the High Seas, resonates with the leitmotif of events in multiple jurisdictions across Asia as the Japanese forces swept through and conquered large swathes of Asia in the 1930s and 1940s. This chapter's objective is to engage with the war crimes aspects of the trials held in Hong Kong, and to extract a deeper understanding from the cases themselves, a major task given the serious limitations that the lack of reasoned judgments poses. The majority of the Hong Kong cases actually involved war crimes against civilians. This category of war crimes raises some good substantive issues for closer consideration (involuntary displacement/deportation, torture and other ill-treatment, and unlawful killing of civilians). This study deliberately centralizes the Hong Kong cases; the objective is to excavate a forgotten legal process and shed light on the law of war crimes as it emerges from these cases. Before moving to war crimes against civilians in occupied territory, this chapter first establishes the sources of the law of war crimes relied on in these Hong Kong trials.