It is said that Buddhism was firstly introduced to Thailand from India during the reign of Ashoka (304-232 BC) when the world famous Indian King sent Buddhist missionaries to lots of places far and wide. However, there was another saying the Buddhism first reached Thailand centuries later. No matter when was the exact dates, the Buddhism reached Thailand, it became the dominant religion very soon. With time came to the Sukhothai period in the 13th century, Theravada Buddhism became official religion in Thailand. Since then, all of kings of Thailand have been Buddhist until now.
Theravada Buddhism is technically considered a philosophy rather than a religion, however, Thai Buddhism has many spiritual beliefs which may be the result of lingering animist and Hindu beliefs centuries ago. So you can see there is a 'spirit house' just outside of Thai people's house or places of business. People make offerings to appease the spirits those might live in their houses or workplaces. Furthermore, Buddhist monks are often invited to give blessing to the spirits to the new houses. And Thai people frequently light incense and pray to Buddha images and a host of Hindu gods whose shrines are found throughout the country.
By its very nature, Buddhism is a compassionate and tolerant religion and the aim of it is alleviating the suffering. So, Buddhism believers in Thailand are very respectful of different religious beliefs and very open toward discussing the values of Buddhist with others. Most Thai peoples believe in reincarnation. Buddha taught that suffering is caused by desires, craving and the human ego and the way to achieve freedom and enlightenment can be through self-awakening and following the Eight-fold Noble Path and a person achieves a state of freedom from suffering and ego, called Nirvana and most Thai people believe that it will take many lifetimes. People seek to improve their standing and closeness to Nirvana in next lifetime by merit-making practices such as giving donations to temples, praying with lighting incense, or alms giving to the monks.
Buddhism in Thailand affects many aspects of Thai life. The senior monks are highly respected and you will often see their images adorned on the walls of business places or homes or even upon ornamented inside of taxi cabs. The wat (temple) in the neighborhood of the villages or towns is the heart of social and religious life. Thai people will go to the wat to pay homage to the Buddha and give alms to monks regularly during the Buddhist holidays or the important days to make merit for themselves.
There are nearly 30,000 temples or wats in Thailand. No matter elaborated and grand or small complexes in the village are more than just places of worship but the one cornerstone of Thai religious life. They are the centers of celebrations, libraries of religious works, house of monks, schools and gathering places for locals and there are featured markets just outside of the temple. The famous Wat Pho even has a Thai massage school on its grounds.
There are around 300,000 monks living in Thailand and when you travel to Thailand, you are almost guaranteed to see some of them. Their yellow and orange robes are very easy to recognize from modern-day clothing. On the street, in the morning, you can see many Thais will start their day off by giving offerings to monks who are collecting donations. Most of young men in Thailand are required to be monks for a period of time. Living a monastic life, even for only a few months, is considered a very important part of life of a man.