The practice of Christianity in Korea is marginal in North Korea, but significant in South Korea, where it revolves around Protestantism and Catholicism, accounting for 8.6 million and 5.8 million members, respectively. The initial variety of Christianity in the peninsula, Nestorianism, spread to Korea in the Middle Ages by way of China via Middle Eastern adherents to the Church of the East. Catholicism was first introduced during the late Joseon Dynasty period by Confucian scholars who encountered it in China. In 1603, Yi Su-gwang, a Korean politician, returned from Beijing carrying several theological books written by Matteo Ricci, an Italian Jesuit missionary to China. He began disseminating the information in the books, introducing Christianity to Korea. In 1758, King Yeongjo of Joseon officially outlawed Catholicism as an "evil practice." Catholicism was reintroduced in 1785 by Yi Seung-hun and French and Chinese Catholic priests were soon invited by the Korean Christians.

Religion in South Korea is diverse. Most South Koreans have no religion. Buddhism and Christianity are the dominant confessions among those who affiliate with a formal religion. Buddhism, which arrived in Korea in 372 AD, has thousands of temples built across the country.