According to the legend, Hinayana was very popular in ancient Funan from about the first or 2^nd century AD, but used the Sanskrit Canon. The traditional belief is that Mahadhammarakkhita and Maharakhita introduced Buddhism to Thailand during the reign of Emperor Asoka in the 3^rd century BC.

From the 6^th century onwards Theravada Buddhism flourished in the lower Menam valley and it continued to be the dominant religion there. But when the lower Menam valley came under the control of the Khmer rulers who were ardent patrons of Brahmanism and Mahayana Buddhism, but Theravada still continued to flourish there.

Dvaravati was a flourishing kingdom of Mon people in the 7^th century. The political influence of the Dvaravati kingdom extended as far as Northern Thailand. The Haripunjaya kingdom of the upper Menam valley was an important kingdom in northern Thailand. Towards the second half of the 7^th century AD Theravada Buddhism was introduced into Haripunjaya.

About the 8^th or 9^th century AD, both Thailand and Laos formed part of Kambuja (Cambodia). Both the Brahmanical religion and Buddhism can be found flourishing side by side in all these regions.

Theravada Buddhism flourished in the lower Menam valley under the patronage of the rulers of the Dvaravati kingdom. Both Mahayanism and Brahmanism existed at the lower Menam valley under the patronage of the Khmer rulers. Towards the beginning of the 13^th century AD, the Haripunjaya kingdom had become a center of Theravada Buddhism. Thus, before the Thais established their contact with Sri Lanka.

About the middle of the 13^th century AD, the Thais made themselves masters of Siam and Laos and put an end to the political supremacy of the Cambodian over them. Sukhodaya was established in central Thailand as the capital of Thai kingdom in the second half of the 13^th century. A king named Rocaraja of Sukhodaya sent an embassy to the king of Sri Lanka requesting him to send the miraculous Sihala Buddha image to Sukhodaya. The king's request was granted and Sukhodaya received its first Buddha image from Sri Lanka.

Around 1317-1347 AD Burma acted as an intermediary between Sri Lanka and Thailand in the religious intercourse. At the request of Lothai, the king of Sukhodaya, Udumbara Mahasami sent the Elder Sumana to establish the Sinhalese form of the monastic discipline and in order to reorganize and model the Buddhist Sangha of Thailand on that of Sri Lanka. In his reign a Thai prince assumed the yellow robe and made a journey to India and Sri Lanka, from which countries he claims to have brought back miraculous relics. A few years later, Kilana, the king of Nabbisipura requested Udumbara Mahasami to send a monk capable of performing all religious acts. As a consequence Ananda thera was sent to Nabbisipura. At the advice of Ananda thera, the king of Nabbisipura then requested the king of Sukhodaya and invited Elder Sumana to his kingdom. In this way, king Kilana and Sumana contributed to the establishment of the Sihala Sangha in northern Thailand.

King Luthai /Lo Thai (1347 AD, son of king Lothai) was not only a great patron of Buddhism, but himself adopted the life of a buddhist monk, preaching the doctrines of the Buddha all over his kingdom. About 1361 AD he sent some learned monks and scholars to Sri Lanka and induced the great monk called Mahasami Samgharaja to come to Thailand. Under his inspiration and the active efforts of the king, Buddhism and Pali literature spread to a number of small Hinduized states in the territories now called Laos. One of his inscriptions, which gives him the tittle of Sri Suryavamsa Rama Mahadharma Rajadhiraja furnishes a long account of the reception accorded to a hierarchy from Sri Lanka invited to Thailand to reorganize the religious institutions there. As a result, Sukhodaya became a great center of Buddhist studies in the middle of the 14^th century AD. From the second half of the 14^th century onwards Buddhism flourished in Thailand and the neighboring regions, and Brahmanism declined until it almost disappeared. A sacred and authentic relic of the Buddha was brought to Thailand from Sri Lanka and it was installed with great solemnity by the king at Nagara Jum. A branch of the sacred Bo-tree was brought to Thailand from Sri Lanka and was planted near this sacred relic at Nagara Jum.

The establishment of the new kingdom of Ayuthia in the middle of the 14^th century and the change of the political center of Thai power from Sukhodaya to Ayuthia marked the beginning of a new era of great cultural prosperity. Under royal patronage Buddhism flourished and Ayuthia became an important Buddhist center. Strong religious ties existed between Sri Lanka and Thailand.

During the reign of Tissaraja (1401-1442 AD) 25 monks went from Nabbisipura together with 8 monks from Cambodia went to Sri Lanka to receive the upasampada ordination and over there they were joined by six monks from the Ramanna country. These 39 monks studied the sacred texts thoroughly and also learned the correct manner of recital of the sacred texts from the Buddhist monks in Sri Lanka. They also took with them the sacred relic of the Buddha. After their arrival at Ayuthia in southern Thailand, the king received them, and they ordained the local monks and established the Sihala Sangha in Thailand. The Sihala fraternity of the monks also introduced to Thailand a higher standard of Pali scholarship.

Tissaraja's son, Tilokaraja / Tilakaraja (1442-1487 AD) himself entered the Sangha in 1447 AD for sometime and with the permission of his teacher he assumed office again as king. In 1455 AD a seedling grown from the southern branch of the Mahabodhi at Anuradhapura was planted by King Tilakaraja at Nabbisipura (Chieng Mai). It is said that Tilakaraja convoked a great council in the Mahabodhi Arama at Nabbisipura in 1475 AD to revise the Pali scriptures. This council is known as the Eighth Buddhist Council in the history of Buddhism in Thailand.

Emperor Tilakapanattu (1495-1525 AD) is regarded as one of the greatest kings of Thailand. He also installed a great Buddha statue in the uposatha hall at the Pubbarama. At the time of the installation important ceremonies were held and he gave dana to several thousand monks who belonged to the Sihala sect, the Nagaravasigana, and the Puppharamavasigana. Among the three fraternities, the Sihala sect became very prominent in Thailand and it took the leading part in all the ecclesiastical acts and performed the acts before as well as after the other fraternities participated in them. In 1515 AD the king conferred the title of Rajaguru (Royal Teacher) on the Mahasami of the Rattavanamahavihara, which is another indication of the importance of the Sihala sect in Thailand. The patronage extended to many scholars and scholarly institutions resulted in the existence of several well-organized educational and religious institutions in the country.

King Maha Dhammaraja II (Boromokot) ascended the throne of Ayuthia in 1733 AD. During his rule Ayuthia became a great center of Buddhism and religious mission from Sri Lanka came there to get help and assistance from the Thai monks. About 1750 AD, the king of Sri Lanka sent messenger to the king of Thailand and the latter sent golden and silver images of the Buddha, copies of sacred texts and about 10 monks under the leadership of Upali Mahathera. It is clear that at that time Sri Lanka recognized Thailand to be a country where Buddhism prevailed in a much purer form.

The Burmese invaders destroyed most of Ayuthia in 1767. As a result of the repeated attacks of the Burmese, the rulers of Thailand shifted their capital to Banckok. General Chakri, who was known as Ramal (1782-1809 AD), was the founder of the present reigning dynasty at Bangkok. Buddhism continued to flourish under the patronage of the rulers of this dynasty.

In 1828, Thailand's Prince Mongkut (later King Rama IV) founds the Dhammayut movement, which later became the Dhammayut Sect.

In 1900, Ven. Ajaan Mun and Ven. Ajaan Sao revive the forest meditation tradition in Thailand.

In the early 19^th century, to prevent the encroachment of Christian missionaries, Rama V (1868-1910) worked with his brothers (one of whom was Prince Mongkut) to move the country from a loose feudal system to a centralized nation-state. By doing that, they enacted religious reforms to present a united front in the face of imperialist threats from Britain and France. This Sangha Act formally marked the beginnings of the Mahanikaya and Dhammayut sects. Sangha government, which up to that time had been in the hands of a lay official appointed by the king, is handed over to the bhikkhus. It wasn't until the 1950's that the movement he founded gained acceptance in Bangkok, and only in the 1970's did it come into prominence on a nationwide level.

The mores and rites handed down over the centuries from teacher to teacher with little reference to the Pali Canon. It was chiefly from the Mons and the Burmese rather than directly from India that the Thais took their Theravada Buddhism and the other Indian elements in their culture as they moved southwards into mainland Southeast Asia.

Hindu deities and many Bra manic practices were retained in Thai Buddhism, most notably in the coronation rites of the royal ceremonies. Many of the fundamental features of Hindu cosmography were incorporated into Buddhist cosmography as well. The Thais also retained many of the ancient animist beliefs and practices from before they first migrated into Southeast Asia. These believes include paying respect to the spirits (phi) of the ancestors and the spirits of place, who live in hills, springs, trees and caves and who protect their houses, shops, villages and cities.

The Tantric elements in early Khmer Mahayana Buddhism is shown by the presence of relief carvings of the Buddha Vajrasattva and of the jina Buddha's in Thailand. The last ten lives, known in Thai as Thotsachat or Sip chat, are the most often illustrated, and of these the last of all, the Vessantara jataka (Thai, Mahachat, 'Great Life'), the life of the supremely charitable Prince Vessantara is the most popular with the Mahayana doctrine.

As early as 17^th century the wat, as a Tai creation, was already taken for granted as the basic unit of the Thai Sangha and the center of lay Buddhism. Joining monastery and shrine creates a social whole that is a community in itself and often the center of a lay community. Only few wat can support themselves and ignore popular wants, the vast majority had to accommodate local interests. That brought the monks into the very heart of the local community and fostered what we might call wat Buddhism. The implication is that monks live a sedentary life in the village monastery, serving the local villagers as doctors or fortune tellers. Monastic discipline tended to be loose.

Occasionally, monks would go on a pilgrimage ("dhutanga") which bore little resemblance to the classic dhutanga practices. In a wat, monks and lay people practiced forms of meditation that deviated from the path of tranquility and insight outlined in the Pali canon. This practices is called vichaa aakhom or incantation knowledge. It involves initiations and invocations used for shamanistic purposes, such as protective charms and magical powers. The nirvana is not mentioned in the teaching except as an entity to be invoked for shamanic rites.

Mahanikaya literally means " the Great branch ". It may be compared to the Mahavihara in ancient Ceylon.

King Mongkut (King Rama IV) sought to give monastic life its former strictness, thus he founded a new movement within the Order and called it the Dhammayattika sect to distinguish it from the original Sangha, which was later called the Mahanikaya sect.

Time went on and both sects have changes and improvements so presently these two sects do not differ substantially in any way from each other. They all belong to Theravada and follow the conservative way of the study and practice of the disciplinary and doctrinal tenets. Both sects have the same Supreme Council of Ecclesiastical Administration presided over by His Holiness the Supreme Patriarch who may be appointed by His Majesty the King of Thailand. The Supreme Patriarch may belong to any sect as the case may be.

Dhammayut literally means "In Accordance with the Dhamma". This sect based on the Pali canon and begun in the 1820's by Prince Mongkut at the time was Reform Buddhism. Institutionally this movement changed Buddhism from a wat-localized to a Sangha-centred religion. Lay religiosity is moving the same way.

Prince Mongkut studied the canon during his early years as a monk. He grew discouraged by the level of practice he saw around him in Thai monasteries, and later re-ordained from the Mons, an ethnic group that straddled the Thai-Burmese border, where he studied Vinaya and the classic dhutanga practices under the guidance of a Mon teacher. Later, his brother, King Rama III, complained that it was disgraceful for member of the royal family to join an ethnic minority, and so built a monastery for the Prince-Monk on the Bangkok side of the river. There, Mongkut attracted a small but strong following of like-minded monks and lay supporters, and in this way the Dhammayut movement was born. After twenty-seven years of monk life, prince Mongkut ascended the throne and became King Rama IV (portrayed in the musical The King and I) after his brother's death in 1851. Rama IV later sponsored the building of new Dhammayut centers in the capital and the provinces, which was how -- by the time of Ajaan Mun -- there came to be a handful of Dhammayut monasteries in Ubon.

In its early years, the Dhammayut movement was an informal grouping devoted to Pali studies, focusing on Vinaya, the classic dhutanga practices, a rationalist interpretation of the Dhamma, and the revival of meditation techniques taught in the Pali canon, such as recollection of the Buddha and mindfulness of the body. But in reality Bangkok encouraged Pali scholarship but ignored meditation.

Mongkut and the movement's members could not prove the teachings of the Pali canon actually led to enlightenment but believed a great deal of merit could revive the earliest Buddhist traditions. Therefore Mongkut and many of his students took a bodhisattva vow and dedicated the merit of his efforts to future Buddhahood.

In terms of Sangha system, the Reform Buddhism movement pulled monks toward the center (Bangkok) by rewards while regulations reached out into the countryside. Rewards such as title, honor, position, and gift encouraged reform and allowed the Sangha government to control monks and wat. Administrative monks owned titles and encouraged by well kept temples and so wat prospered physically.