The Japan Self-Defense Forces (Japanese: 自衛隊, Hepburn: Jieitai; JSDF) are the military forces of Japan. Established in 1954, the JSDF comprises the Japan Ground Self-Defense Force, the Japan Maritime Self-Defense Force, and the Japan Air Self-Defense Force. They are controlled by the Ministry of Defense with the Prime Minister as commander-in-chief.

Since the end of the Cold War, and particularly into the 21st century, increased tensions with North Korea, China, and Russia have reignited debate over the status of the JSDF and their relationship to Japanese society. The JSDF have prioritized greater cooperation and partnership with Australia, India, Taiwan, South Korea, Singapore, the United Kingdom, the United States, and NATO, as well as acquiring new equipment and hardware.

Japan surrendered to the Allied Powers on 15 August 1945, and officially exchanged instruments of surrender in Tokyo Bay on 2 September, after which Japan underwent a U.S.-led military occupation for seven years, until 28 April 1952. The Occupation was commanded by American general Douglas MacArthur, whose office was designated the Supreme Command for the Allied Powers (SCAP). In the initial phase of the occupation, from 1945 to 1946, SCAP had pursued an ambitious program of social and political reform, designed to ensure that Japan would never again be a threat to world peace.

Among other reforms, SCAP worked with Japanese leaders to completely disband the Japanese military. In addition, SCAP sought to unravel the wartime Japanese police state by breaking up the national police force into small American-style police forces controlled at the local level. SCAP also sought to empower previously marginalized groups that it believed would have a moderating effect on future militarism, legalizing the Communist and Socialist parties and encouraging the formation of labor unions. The crowning achievement of the first phase of the occupation was the promulgation at SCAP's behest in 1947 of a new Constitution of Japan. Article 9 of the Japanese Constitution explicitly disavows war as an instrument of state policy and promises that Japan will never maintain a military as well as other war potential.

By this time, Cold War tensions were already ramping up in Europe, where the Soviet occupation of Eastern European countries led Winston Churchill to give his 1946 "Iron Curtain" speech, as well as in Asia, where the tide was turning in favor of the Communists in the Chinese Civil War. These shifts in the geopolitical environment led to a profound shift in U.S. government and Allied Occupation thinking about Japan, and rather than focusing on punishing and weakening Japan for its wartime transgressions, the focus shifted to rebuilding and strengthening Japan as a potential ally in the emerging global Cold War, leading to a reversal of many earlier Occupation policies that has come to be known as the "Reverse Course." As part of this shift, MacArthur and other U.S. leaders began to question the wisdom of having insisted upon Japan renouncing all military capabilities. These sentiments were intensified in 1950 as Occupation troops began to be moved to the Korean War (1950–53) theater. This left Japan defenseless and vulnerable, and caused U.S. and Japanese conservative leaders alike to becoming increasingly aware of a pressing need to enter a mutual defense relationship with the United States in order to guarantee Japan's external security in the absence of a Japanese military. Meanwhile, on the Japanese domestic front, rampant inflation, continuing hunger and poverty, and the rapid expansion of leftist parties and labor unions led Occupation authorities to fear that Japan was ripe for communist exploitation or even a communist revolution and to believe that conservative and anti-communist forces in Japan needed to be strengthened. Accordingly, in July 1950, Occupation authorities authorized the establishment of a National Police Reserve (警察予備隊, Keisatsu-yobitai), consisting of 75,000 men equipped with light infantry weapons. In 1952, the Coastal Safety Force (海上警備隊, Kaijō Keibitai), the waterborne counterpart of NPR, was also founded.

The Security Treaty Between the United States and Japan was signed on 8 September 1951 and came into force on 28 April 1952. While the treaty allowed the United States to maintain military bases in Japan, it did not obligate US forces to defend Japan should Japan come under attack. As left-wing protests in Japan remained a major concern to Japanese and American leaders alike, the treaty explicitly allowed US military forces based in Japan put down "internal riots and disturbances" in Japan. In addition, in mid-1952, the National Police Reserve was expanded to 110,000 men and named the "National Safety Forces." Along with it, the Coastal Safety Force was moved to the National Safety Agency to start a de facto navy.

(1) Aspiring sincerely to an international peace based on justice and order, the Japanese people forever renounce war as a sovereign right of the nation and the threat or use of force as means of settling international disputes.
(2) In order to accomplish the aim of the preceding paragraph, land, sea, and air forces, as well as another war potential, will never be maintained. The right of belligerency of the state will not be recognized.

Meanwhile, the Japanese government began a long and ongoing process of gradually reinterpreting Article 9 of the Japanese Constitution to allow greater and greater military capabilities, under the interpretation that Article 9 disallowed offensive warmaking capabilities but did not necessarily deny the nation the inherent right to self-defense. These reinterpretations were avidly encouraged by the government of United States, which hoped that by remilitarizing Japan would be able to take up more of the burden for its own self-defense. This reinterpretation of Article 9 cleared the way for the creation of a Defense Agency and the transformation of the National Security Force into a "Self-Defense Force" that would be a military in all but name.