The Kuomintang (KMT), also referred to as the Guomindang (GMD), the Nationalist Party of China (NPC) or the Chinese Nationalist Party (CNP), is a major political party in the Republic of China, initially on the Chinese mainland and then in Taiwan since 1949. It was the sole ruling party in China during the Republican Era from 1928 to 1949, when most of the Chinese mainland was under its control. The party retreated from the mainland to Taiwan on 7 December 1949, following its defeat in the Chinese Civil War. Chiang Kai-shek declared martial law and retained its authoritarian rule over Taiwan under the Dang Guo system until democratic reforms were enacted in the 1980s and full democratization in the 1990s.

The party originated as the Revive China Society, founded by Sun Yat-sen on 24 November 1894 in Honolulu, Hawaii. From there, the party underwent major reorganization changes that occurred before and after the Xinhai Revolution, which resulted in the collapse of the Qing dynasty and the establishment of the Beiyang government. In 1919, Sun Yat-sen re-established the party under the name Kuomingtang in the Shanghai French Concession. In December 1912, an election was held, and Song Jiaoren was instrumental in ensuring victories for his party, the Kuomintang. It was widely thought that Song would become the next prime minister. However, Song was assassinated. In the summer of 1913, seven southern provinces rebelled because they felt that Yuan Shikai was responsible for the assassination of Song Jiaoren and because they felt he obtained his position through political manipulation rather than merit and so started the Second Revolution

From 1926 to 1928, the KMT under Chiang Kai-shek successfully led the Northern Expedition against regional warlords and unified the fragmented nation that developed during the Warlordism Era. From 1937 to 1945, the KMT-ruled Nationalist government led China through the Second Sino-Japanese War against Japan. By 1949, the KMT was decisively defeated by the Chinese Communist Party (CCP) in the Chinese Civil War (in which the People's Republic of China was established by the CCP on 1 October 1949) and withdrew the ROC government to Taiwan, a former Qing territory annexed by the Empire of Japan from 1895 to 1945.

The decade of 1928-37 was one of consolidation and accomplishment by the KMT. Some of the harsh aspects of foreign concessions and privileges in China were moderated through diplomacy. The government acted energetically to modernize the legal and penal systems, stabilize prices, amortize debts, reform the banking and currency systems, build railroads and highways, improve public health facilities, legislate against traffic in narcotics, and augment industrial and agricultural production. Great strides also were made in education and, in an effort to help unify Chinese society, in a program to popularize the national language and overcome dialectal variations. The widespread establishment of communications facilities further encouraged a sense of unity and pride among the people.

From 1949 to 1987, the KMT ruled Taiwan as an authoritarian one-party state after the February 28 incident. During this period, martial law was in effect and civil liberties were curtailed under the guise of anti-communism, with the period being known as the White Terror. The party oversaw Taiwan's economic development, but also experienced diplomatic setbacks, including the ROC losing its United Nations seat and most of the world including its ally the United States switching diplomatic recognition to the CCP-led People's Republic of China (PRC) in the 1970s. In the late 1980s, Chiang Ching-kuo, Chiang Kai-shek's son and the next KMT leader in turn, lifted martial law and allowed the establishment of opposition parties such as the DPP. His successor Lee Teng-hui continued pursuing democratic reforms and constitutional amendments, and was re-elected in 1996 through a direct presidential election, the first time in the ROC history.