Japan maintains close economic and military relations with its key ally the United States, with the U.S.-Japan security alliance serving as the cornerstone of its foreign policy. A member state of the United Nations since 1956, Japan has served as a non-permanent Security Council member for a total of 19 years, most recently in 2009. It is also one of the G4 nations seeking permanent membership in the Security Council. As a member of the G8, the APEC, the "ASEAN Plus Three" and a participant in the East Asia Summit, Japan actively participates in international affairs and enhances diplomatic ties with its important partners around the world. Japan signed a security pact with Australia in March 2007 and with India in October 2008. It is also the world's third largest donor of official development assistance after the United States and United Kingdom, donating US$8.86 billion in 2004. Japan contributed non-combatant troops to the Iraq War but subsequently withdrew its forces from Iraq.

Japan is engaged in several territorial disputes with its neighbors: with Russia over the South Kuril Islands, with South Korea over the Liancourt Rocks, with the People's Republic of China and Taiwan over the Senkaku Islands, and with the PRC over the EEZ around Okinotorishima.

Japan also faces an ongoing dispute with North Korea over its abduction of Japanese citizens and its nuclear weapons and missile program (see also Six-party talks). As a result of the Kuril Islands dispute, Japan is technically still at war with Russia since no treaty resolving the issue was ever signed.

Japan's military is restricted by the Article 9 of the Japanese Constitution, which renounces Japan's right to declare war or use military force as a means of settling international disputes. Japan's military is governed by the Ministry of Defense, and primarily consists of the Japan Ground Self-Defense Force (JGSDF), the Japan Maritime Self-Defense Force (JMSDF) and the Japan Air Self-Defense Force (JASDF). The forces have been recently used in peacekeeping operations and the deployment of Japanese troops to Iraq marked the first overseas use of its military since World War II.