The alliance between Japan and the United States, one of the great "success stories" of the postwar world, has come under considerable academic scrutiny in the last decade. Academic attention has been stimulated by the rapidly changing regional environment, most notably the rise of China and the North Korean nuclear program; and by the evolving political scene in Japan, most importantly the activist and iconoclastic leadership of Prime Minister Koizumi. The recent collapse of the Liberal Democratic Party (LDP) and the inauguration a Democratic Party of Japan (DPJ) government under Prime Minister Hatoyama with a different vision of the Japan-U.S. alliance and Japan's role in the world has launched a new round of journal articles, many challenging some of the assumptions of the earlier analysis about the likely evolution of Japan-U.S. relations and Japan's foreign policy. Most of the recent analysis of the alliance and Japan has been focused on the broad political, economic, and demographic trends that are shaping the external and internal environment. There has been little examination of the institutional changes in Japan that both reflect the evolution in Japan's security policy to date and provide new capabilities and legal flexibility for Japan to take on an expanded military role in the future. This volume fills this void with a comprehensive and multidimensional analysis that links the historical evolution of Japan's security policies to its current capabilities and prospects.