The traditional Korean calendar is a lunisolar calendar, like the traditional calendars of other East Asian countries. Dates are calculated from Korea's meridian, and observances and festivals are based in Korean culture.

The Gregorian calendar was officially adopted in 1896, but traditional holidays and age-reckoning for older generations are still based on the old calendar. The biggest festival in Korea today is Seollal, the first day of the traditional Korean New Year. Other important festivals include Daeboreum also refer to as Boreumdaal (the first full moon), Dano (spring festival) and Chuseok (harvest moon festival), and Samjinnal (spring-opening festival). Other minor festivals include Yudu (summer festival), and Chilseok (monsoon festival).

See also Public holidays in North Korea and Public holidays in South Korea.

The traditional calendar designated its years via Korean era names from 270 to 963. Then Chinese era name with Korean era names were used few times until 1894. In 1894-1895, The lunar calendar was used with years numbered from the foundation of the Joseon Dynasty in 1392.

The Korean War (Korean: 한국전쟁 or 조선전쟁, Hanja: 韓國戰爭 or 朝鮮戰爭; 25 June 1950 – 27 July 1953) was a war between the Republic of Korea (supported primarily by the United States of America, with contributions from allied nations under the aegis of the United Nations) and the Democratic People's Republic of Korea (supported by the People's Republic of China, with military and material aid from the Union of Soviet Socialist Republics). The Korean War was primarily the result of the political division of Korea by an agreement of the victorious Allies at the conclusion of the Pacific War at the end of World War II. The Korean Peninsula was ruled by the Empire of Japan from 1910 until the end of World War II. Following the surrender of the Empire of Japan in September 1945, American administrators divided the peninsula along the 38th parallel, with U.S. military forces occupying the southern half and Soviet military forces occupying the northern half.