Approximately 95% of the Thai citizens are Theravada Buddhists. The Thais themselves frequently call their religion Lankavamsa (Sinhalese lineage) Buddhism because Thailand originally received Buddhism from Sri Lanka during the Sukhothai period. Strictly speaking, Theravada refers only to the earliest forms of Buddhism practised during the Ashokan and immediate port-Ashokan periods in South Asia. The early Dvaravati and pre-Dvaravati forms of Buddhism - those which existed up until the 10th or 11th century - are not the same as that which developed in Thai territories after the 13th century.
Since the Sukhothai period (13th to 15th centuries), Thailand has maintained an unbroken canonical tradition and 'pure' ordination lineage, the only country among the Theravadin countries to have done so. Ironically, when the ordianation lineage in Sri Lanka broke down during the 18th century under Dutch persecution, it was Thailand that restored the Sangha (Buddhist brotherhood) there. To this day the major sect in Sri Lanka is called Siamopalivamsa (Siam-Upali lineage, Upali being the name of the Siamese monk who led the expedition to Ceylon), or simply Siam Nikaya (the Siamese sect).
Basically, the Theravada school of Buddhism is an earlier and, according to its followers, less corrupted form of Buddhism than the Mahayana schools found in East Asia or in the Himalayan lands. The Theravada (literally, 'teaching of the elders') school is also called the 'southern' school since it took a southern route from India, its place of origin, through South-East Asia (Mynmar, Thailand, Laos and Cambodia in this case), while the 'northern' school proceeded north into Nepal, Tibet, China, Korea, Mongolia, Vietnam and Japan.
Because the Theravada school tried to preserve or limit the Buddhist doctrines to only those canons codified in the early Buddhist era, the Mahayana school gave Theravada Buddhism the name Hinayana, or the 'lesser vehicle'. The Mahayana school was the 'great vehicle', because it built upon the earlier teachings, 'expanding' the doctrine in such a way as to respond more to the needs of lay people, or so it is claimed.
The Buddha taught his disciples :
When you see, just see.
When you hear, just hear.
When you smell, just smell.
When you touch, just touch.
When you know, just know.
Many Thais express the feeling that they are somehow unworthly of nibbana. By feeding monks, giving donations to temples and performing regular worship at the local 'wat' (temple) they hope to improve their lot, acquiring enough merit (Pali term 'punna' ; Thai term 'bun') to prevent or at least lessen the number of rebirths. The making of merit ('tham bun') is an important social and religious activity in Thailand. The concept of reincarnation is almost universally accepted in Thailand, even by non-Buddhists, and the Buddhist theory of karma is well expressed in the Thai proverb 'tham dii, dai dii : tham chua, dai chua' (do good and receive good ; do evil and receive evil).
The Triratna, or Triple Gems, highly respected by Thai Buddhists, include the Buddha, the Dhamma (the teachings) and the Sangha (the Buddhist brotherhood). All are quite visible in Thailand. The Buddha, in his myriad and omnipresent sculptural forms, is found on a high shelf in the lowliest roadside restaurants as well as in the lounges of expensive Bangkok hotels.
The Dhamma is chanted morning and evening in every 'wat' and taught to every Thai citizen in primary school. The Sangha is seen everywhere in the presence of orange-robed monks, especially in the early morning hours when they perform their alms-rounds, in what has almost become a travel-guide cliche in motion.
Thai Buddhism has no particular 'Sabbath' or day of the week when Thais are supposed to make temple visits. Nor is there anythings corresponding to a liturgy or mass over which a priest presides. Instead Thai Buddhists visit the 'wat' whenever they feel like it, most often on 'wan phra' (literally, 'excellent days'), which occur with every full and new moon, ie every 15 days.
Suan Mok, a 120-acre forest temple in Chaiya district, Surat Thani province, some 580 kilometres south of Bangkok, attracts and accepts meditators from all over the world. Meditation opportunities are also found in Bangkok, particularly at Wat Mahathat (facing Sanam Luang), \A/at Pak Nam, Wat Chonprathan Rangsit, Wat Phrathammakai and Banglamphu's Wat Bowon Nivet where English-language instruction is available.