The Imperial Japanese Army imposed martial law (gunritsu) in areas occupied during each of the full-scale conflicts it fought between 1894 and 1945. This article traces changes and continuities in the purpose, function, and content of martial law during the First Sino-Japanese War, the Russo-Japanese War, and the Asia-Pacific War to advance our historical knowledge of a much-understudied aspect of Japanese warfare. In so doing, it details the development and evolution of martial law as an instrument of military power showing how regulations were also influenced by and, therefore, tended to reflect the different wartime priorities and macro-level policies of the (military) leadership. It also highlights that the character of martial law remained largely unchanged and reveals that many of the legal practices utilized during the Asia-Pacific War were rooted in earlier conflicts. It ultimately argues, however, that wartime context and immediate military objectives took precedence over any longer-term political ambitions in Asia and, more crucially, over the welfare of civilians under occupation.