This article introduces readers to World War ii-era Japanese primary sources that have become available, over the last three decades, at the major archives and libraries. It also illustrates how and why some of these hitherto unavailable archival materials have become publicly accessible. At first, political, diplomatic and military historians primarily conducted their research at Diplomatic Archives, Military Archives, and the Modern Japanese Political History Materials Room, until the Japanese Diet passed a law in 2011 stipulating that all government and agencies, except for the Foreign Ministry and Imperial Household Agency, must transfer archived documents to the National Archives of Japan (naj). Enhancing its importance for research, the naj played the lead role in creating and maintaining the Japan Center for Asian Historical Records that has sustained a major effort at digitization. Other important primary sources include documents related to Emperor Hirohito, the Documents on Japanese Foreign Policy series, holdings of the Military History Department, and materials non-governmental organizations have published. The amount of Japanese source materials and their digitization now has reached a level that meets the U.S. and European standards.