Sukjong (Korean: 숙종; Hanja: 肅宗; 7 October 1661 – 12 July 1720), personal name Yi Sun (이순; 李焞), was the 19th monarch of the Joseon dynasty of Korea.

King Sukjong was a brilliant politician, but his reign was marked by some of the most intense factional fights in the Joseon dynasty.

With each change of government, which was called hwanguk (Korean: 환국; Hanja: 換局), literally change/switching of the state, the losing faction was completely driven out of politics with executions and exiles.

Nevertheless, the chaotic changes of government did not affect the general populace significantly, and his reign is considered one of more prosperous times.

Sukjong died in 1720 supposedly after telling Yi Yi-myoung to name Prince Yeoning as Gyeongjong's heir - in absence of a historiographer or recorder.

Sukjong's accomplishments include tax reform (大同法), the creation of a new monetary system and currency (Korean mun), and the liberalization of civil service rules promoting the middle class and children of concubines into higher-ranking regional government positions.

In 1712, Sukjong's government worked with the Qing Dynasty in China to define national borders between the two countries at the Yalu and Tumen Rivers.

He was buried in Myeongneung (명릉) in Goyang, Gyeonggi Province, inside the Five Western Royal Graves (서오릉, 西五陵; Seooneung).