In 1945, Japan and Australia were foes; today they are partners in security, defence and military matters, each the other’s most important strategic ally, after the United States. As the region faces threats from an increasingly assertive China, there is a growing prospect of conflict, particularly in Northeast Asia. McDermott discusses how Japan and Australia may cooperate in mil-itary action. Using previously classified government documents, and interviews with those involved in the decisions, as well as his own experiences, McDermott examines how political imperatives have shaped the security side of the A-JDSR. He offers new insights into the history and future of the relationship. An essential read for students and scholars of Asia-Pacific and Indo-Pacific security.