Historically, Buddhism has been the dominant Religion in Cambodia, however before its introduction Hinduism also flourished. Roman Catholicism was introduced by French missionaries beginning in the eighteenth century. Sunni Islam is practiced among the Chams,while among the Sino-Khmer population Mahayana Buddhism, Confucianism and Chinese folk religions remain popular.
Buddhism has existed in Cambodia since at least the 5th century AD, with some sources placing its origin as early as the 3rd century BC. Theravada Buddhism has been the Cambodian state religion since the 13th century AD (excepting the Khmer Rouge period), and is currently estimated to be the faith of 95% of the population.
The history of Buddhism in Cambodia spans nearly two thousand years, across a number of successive kingdoms and empires. Buddhism entered Cambodia through two different streams. The earliest forms of Buddhism, along with Hindu influences, entered the Funan kingdom with Hindu merchants. In later history, a second stream of Buddhism entered Khmer culture during the Angkor empire when Cambodia absorbed the various Buddhist traditions of the Mon kingdoms of Dvaravati and Haripunchai.
For the first thousand years of Khmer history, Cambodia was ruled by a series of Hindu kings with an occasional Buddhist king, such as Jayavarman I of Funan, and Suryvarman I. A variety of Buddhist traditions co-existed peacefully throughout Cambodian lands, under the tolerant auspices of Hindu kings and the neighboring Mon-Theravada kingdoms.
Cambodia was first influenced by Hinduism during the beginning of the Kingdom of Funan kingdom. Hinduism was one of the Khmer Empire's official religions. Cambodia is the home to one of the only two temples dedicated to Brahma in the world. Angkor Wat of Cambodia is the largest Hindu temple of the world.
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.
The Cham have their own mosques. In 1962 there were about 100 mosques in the country. At the end of the nineteenth century, the Muslims in Cambodia formed a unified community under the authority of four religious dignitaries—mupti, tuk kalih, raja kalik, and tvan pake. A council of notables in Cham villages consisted of one hakem and several katip, bilal, and labi. The four high dignitaries and the hakem were exempt from personal taxes, and they were invited to take part in major national ceremonies at the royal court. When Cambodia became independent, the Islamic community was placed under the control of a five-member council that represented the community in official functions and in contacts with other Islamic communities. Each Muslim community has a hakem who leads the community and the mosque, an imam who leads the prayers, and a bilal who calls the faithful to the daily prayers. The peninsula of Chrouy Changvar near Phnom Penh is considered the spiritual center of the Cham, and several high Muslim officials reside there. Each year some of the Cham go to study the Qur'an at Kelantan in Malaysia, and some go on to study in, or make a pilgrimage to, Mecca. According to figures from the late 1950s, about seven percent of the Cham had completed the pilgrimage and could wear the fez or turban as a sign of their accomplishment.
The first known Christian mission in Cambodia was undertaken by Gaspar da Cruz, a Portuguese member of the Dominican Order, in 1555-1556. According to his own account, the enterprise was a complete failure; he found the country run by a "Bramene" king and "Bramene" officials, and discovered that "the Bramenes are the most difficult people to convert". He felt that no one would dare to convert without the King's permission, and left the country in disappointment, not having "baptized more than one gentile whom I left in the grave".
Despite the French colonization in the 19th century, Christianity made little impact in the country. In 1972 there were probably about 20,000 Christians in Cambodia, most of whom were Roman Catholics. Before the repatriation of the Vietnamese in 1970 and 1971, possibly as many as 62,000 Christians lived in Cambodia. According to Vatican statistics, in 1953, members of the Roman Catholic Church in Cambodia numbered 120,000, making it at the time, the second largest religion, estimates indicate that about 50,000 Catholics were Vietnamese. Many of the Catholics remaining in Cambodia in 1972 were Europeans-chiefly French. Steinberg reported, also in 1953, that an American Unitarian mission maintained a teacher-training school in Phnom Penh, and Baptist missions functioned in Battambang and Siem Reap provinces. A Christian and Missionary Alliance mission was founded in Cambodia in 1923; by 1962 the mission had converted about 2,000 people.
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. In 1982 French geographer Jean Delvert reported that three Christian villages existed in Cambodia, but he gave no indication of the size, location, or type of any of them. 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 weekly service after police harassment. His estimates suggest that in 1987 the Christian community in Cambodia had shrunk to only a few thousand members.
There are around 20,000 Catholics in Cambodia which represents 0.15% of the total population. There are no dioceses, but there are three territorial jurisdictions - one Apostolic Vicariate and two Apostolic Prefectures. The Church of Jesus Christ of Latter-day Saints (also known as the Mormons) has a growing population in Cambodia. The church's late prophet, President Gordon B. Hinckley, officially introduced missionary work to Cambodia on May 29, 1996. The church now has 15 congregations (12 Khmer language and 3 Vietnamese language).
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.
Although most Cambodians adhere to Buddhism or the other main religious groups like Hinduism, Islam and Christianity, there is a strong belief in guardian spirits of the ancestors, Neak Tha, Yeay Mao and many others.