As of 2005, just under half of the South Korean population expressed no religious preference. Of the rest, most are Buddhist or Christian. According to the 2007 census, 29.2% of the population at that time was Christian (18.3% identified themselves as Protestants, 10.9% as Roman Catholics), and 22.8% were Buddhist. Other religions include Islam and various new religious movements such as Jeungism, Cheondoism and Wonbuddhism. The earliest religion practiced was Korean shamanism. Today, freedom of religion is guaranteed by the constitution, and there is no state religion.
Christianity is South Korea's largest religion, accounting for more than half of all South Korean religious adherents. There are approximately 13.7 million Christians in South Korea today, with almost two-thirds of Christians belonging to Protestant churches, while about 37% belong to the Roman Catholic Church. Protestantism has proportionally declined since the 1980s in favour of Roman Catholicism. South Korea is also the second-largest missionary-sending nation, after the United States.
Buddhism was introduced to Korea in the year 372. According to the national census as of 2005, South Korea has over 10.7 million Buddhists. Today, about 90% of Korean Buddhists belong to Jogye Order. Most of the National Treasures of South Korea are Buddhist artifacts. Buddhism was the state religion of Korea from the North South States Period (not to be confused with the modern division of Korea) to Goryeo before suppression under the Joseon Dynasty in favor of Neo-Confucianism.
Fewer than 30,000 South Koreans are thought to be Muslims, but the country has some 100,000 resident foreign workers from Muslim countries, chiefly from Bangladesh and Pakistan