In a historic landslide victory, on August 30, 2009, Japan's largest opposition party, the Democratic Party of Japan (DPJ), ousted the main ruling party, the Liberal Democratic Party (LDP), in elections for control over Japan's Lower House of parliament. The LDP has had almost continuous control of the Japanese government since 1955 and has been a staunch supporter of the U.S.-Japan alliance throughout the postwar period. The DPJ, which includes a mixture of right- and left-leaning members and is led by Yukio Hatoyama, is now Japan's main ruling party. The Diet (Japan's parliament) is expected to elect Hatoyama as Japan's new prime minister in a special Diet session scheduled to begin on September 16. Since 2007, the DPJ has controlled the less powerful Upper House of the Diet, along with two smaller parties, a coalition that is expected to continue once the DPJ officially takes over the government. The DPJ policy platform advocates sweeping economic and administrative reforms and has called for a "proactive" foreign policy with greater "independence" from the United States through deeper engagement with Asia and a more United Nations-oriented diplomacy. In particular, the party has in the past criticized many issues related to the U.S.-Japan alliance, such as plans to realign U.S. forward deployed forces based in Okinawa, Japan's "Host Nation Support" (HNS) payments (worth around $4 billion) that defray much of the costs of American troops and bases in Japan, and the bilateral Status of Forces Agreement (SOFA). In 2007, the DPJ briefly blocked legislation allowing the Japan Maritime Self-Defense Force (JMSDF) to continue the refueling of U.S. and allied vessels engaged in Operation Enduring Freedom (OEF) in Afghanistan. For the United States, the most significant of these issues would be the HNS and base realignment plans. During the campaign for the Lower House elections, the DPJ showed signs of a more pragmatic approach toward the U.S.-Japan alliance in order to deflect LDP criticism that it was not prepared to run the country. The DPJ dropped demands to end the current legislative authorization for the JMSDF refueling mission in the Indian Ocean, and took a slightly more ambiguous position regarding the SOFA and other bilateral alliance management issues. The party's call for a U.N. and Asia-oriented diplomacy also appears to fall short of a more strategic shift to replace the U.S.-Japan alliance with an alternative regional security arrangement. Other signs suggest that the party might indirectly support U.S. foreign policy interests over the long-term through enhanced Japanese contributions to U.N.-sanctioned activities, as well as engagement in regional trade institutions and multilateral fora. Nonetheless, the party remains deeply divided on many foreign policy-related issues and continues to send conflicting signals about its overall approach toward the United States. While a political changeover in Tokyo represents a watershed moment for Japan and potentially for U.S.-Japan relations, the extent to which there will be significant policy changes in Tokyo remains uncertain. It is not clear whether some of the DPJ's past criticism of the U.S.-Japan alliance and other LDP-backed policies was the result of opposition party politicking or more fundamental policy principles that will be implemented now that the party is coming to power. The DPJ faces daunting political and economic challenges at home that many see as a higher priority for the party than its proposals for adjusting the structure of the U.S.-Japan alliance. This report analyzes the DPJ's policy platform and reviews the implications for U.S. strategic and economic interests now that the party and its coalition allies are set to take control of the Japanese government in the wake of the August 30 parliamentary elections.