Korea Train eXpress (KTX) is South Korea's high-speed rail system, operated by Korail. Construction began on the high-speed line from Seoul to Busan in 1992. KTX services were launched on April 1, 2004.

KTX operates from Incheon International Airport with stops at Seoul Station, Yongsan Station towards Busan and Gwangju, and from Gangnam District's Suseo Station with intermediate stations in New Dongtan City and Seoul Subway Line 1's Jije Station in Pyeongtaek. A new line from Wonju to Gangneung was completed in December 2017 to serve the 2018 Winter Olympics in Pyeongchang.

Top speed for trains in regular service is currently 305 km/h (190 mph), though the infrastructure is designed for 350 km/h (217 mph). The initial rolling stock was based on Alstom's TGV Réseau, and was partly built in Korea. The domestically developed HSR-350x, which achieved 352.4 km/h (219.0 mph) in tests, resulted in a second type of high-speed trains now operated by Korail, the KTX Sancheon. The next generation KTX train, HEMU-430X, achieved 421.4 km/h in 2013, making South Korea the world's fourth country after Japan, France and China to develop a high-speed train running on conventional rail above 420 km/h.