South Korea,[b] officially the Republic of Korea (ROK),[c] is a country in East Asia. It constitutes the southern part of the Korean Peninsula and borders North Korea along the Korean Demilitarized Zone.[d] The country's western border is formed by the Yellow Sea, while its eastern border is defined by the Sea of Japan. South Korea claims to be the sole legitimate government of the entire peninsula and adjacent islands. It has a population of 51.96 million, of which roughly half live in the Seoul Capital Area, the fourth most populous metropolitan area in the world. Other major cities include Incheon, Busan, and Daegu.

The Korean Peninsula was inhabited as early as the Lower Paleolithic period. Its first kingdom was noted in Chinese records in the early 7th century BCE. Following the unification of the Three Kingdoms of Korea into Silla and Balhae in the late 7th century, Korea was ruled by the Goryeo dynasty (918–1392) and the Joseon dynasty (1392–1897). The succeeding Korean Empire (1897–1910) was annexed in 1910 into the Empire of Japan. Japanese rule ended following Japan's surrender in World War II, after which Korea was divided into two zones; a northern zone occupied by the Soviet Union and a southern zone occupied by the United States. After negotiations on reunification failed, the southern zone became the Republic of Korea in August 1948 while the northern zone became the communist Democratic People's Republic of Korea the following month.

In 1950, a North Korean invasion began the Korean War, which saw extensive American-led United Nations intervention in support of the South, while China intervened to support the North, with Soviet assistance. After the war's end in 1953, the country entered into a military alliance with the U.S., which continues to this date, and its devastated economy began to soar, recording the fastest rise in average GDP per capita in the world between 1980 and 1990. Despite lacking natural resources, the nation rapidly developed to become one of the Four Asian Tigers based on international trade and economic globalization, integrating itself within the world economy with export-oriented industrialization; currently being one of the largest exporting nations in the world, along with having one of the largest foreign-exchange reserves in the world. The June Democratic Struggle led to the end of authoritarian rule in 1987 and the country is now considered among the most advanced democracies in Asia.

South Korea is a regional power and a developed country, with its economy being ranked as the world's thirteenth-largest by nominal GDP and the fourteenth-largest by GDP (PPP). In recent years, the country has been facing an aging population and the lowest fertility rate in the world. South Korea's citizens enjoy one of the world's fastest Internet connection speeds and the densest high-speed railway network. The country is the world's ninth-largest exporter and ninth-largest importer. Its armed forces are ranked as one of the world's strongest militaries, with the world's second-largest standing army by military and paramilitary personnel. In the 21st century, South Korea has been renowned for its globally influential pop culture, particularly in music (K-pop), TV dramas (K-dramas) and cinema, a phenomenon referred to as the Korean Wave. It is a member of the OECD's Development Assistance Committee, the G20, the IPEF, and the Paris Club.