Cambodia is predominantly Buddhist with 90% of the population being Theravada Buddhist, 1% Christian and the majority of the remaining population follow Islam, atheism, or animism.
Buddhism has existed in Cambodia since at least the 5th century CE Theravada Buddhism has been the Cambodian state religion since the 13th century CE (excepting the Khmer Rouge period), and is currently estimated to be the faith of 90% of the population.
Islam is the religion of a majority of the Cham (also called Khmer Islam) and Malay minorities in Cambodia. According to Po Dharma, there were 150,000 to 200,000 Muslims in Cambodia as late as 1975. Persecution under the Khmer Rouge eroded their numbers, however, and by the late 1980s they probably had not regained their former strength. All of the Cham Muslims are Sunnis of the Shafi’i school. Po Dharma divides the Muslim Cham in Cambodia into a traditionalist branch and an orthodox branch.
Christianity was introduced into Cambodia by Roman Catholic missionaries in 1660. However, it made little headway at first, particularly among Buddhists. In 1972 there were probably about 20,000 Christians in Cambodia, most of whom were Roman Catholics. According to Vatican statistics, in 1953, members of the Roman Catholic Church in Cambodia numbered 120,000, making it, at that time, the second largest religion in the country. In April 1970, just before repatriation, estimates indicate that about 50,000 Catholics were Vietnamese. Many of the Catholics remaining in Cambodia in 1972 were Europeans chiefly French. American Protestant missionary activity increased in Cambodia, especially among some of the hill tribes and among the Cham, after the establishment of the Khmer Republic. The 1962 census, which reported 2,000 Protestants in Cambodia, remains the most recent statistic for the group. Observers reported that in 1980 there were more registered Khmer Christians among the refugees in camps in Thailand than in all of Cambodia before 1970. Kiernan notes that, until June 1980, five weekly Protestant services were held in Phnom Penh by a Khmer pastor, but that they had been reduced to a single weekly service after police harassment. There are around 20,000 Catholics in Cambodia which represents only 0.15% of the total population. There are no dioceses, but there are three territorial jurisdictions one Apostolic Vicariate and two Apostolic Prefectures.
Highland tribal groups, most with their own local religious systems, probably number fewer than 100,000 persons. The Khmer Loeu have been loosely described as animists, but most tribal groups have their own pantheon of local spirits. In general they see their world filled with various invisible spirits (often called yang), some benevolent, others malevolent. They associate spirits with rice, soil, water, fire, stones, paths, and so forth. Sorcerers or specialists in each village contact these spirits and prescribe ways to appease them. In times of crisis or change, animal sacrifices may be made to placate the anger of the spirits. Illness is often believed to be caused by evil spirits or sorcerers. Some tribes have special medicine men or shamans who treat the sick. In addition to belief in spirits, villagers believe in taboos on many objects or practices. Among the Khmer Loeu, the Rhade and Jarai groups have a well developed hierarchy of spirits with a supreme ruler at its head.