The Theravada school is the most conservative of the extant schools of Buddhism and regards its doctrine and practice as close to the original teaching of the Buddha. The Buddha is remembered as one of three refuges of sentient beings, along with the Sangha (the community of monks) and the Dhamma (the teaching). The Buddha is seen as a great human being who came fully to understand the truth of the way things are and therefore to embody that truth. Theravada doctrine is based on the threefold canon of scriptures written in the Pali language. This is made up of the Sutta (the discourses of the Buddha); the Vinaya (the rules which form the basis of Theravadin monastic practice); and the Abhidhamma (the analysis of the doctrinal teaching).
     According to Theravada cosmology, all beings inhabit one of many world systems, all of which have their own heavens and hells, gods and demons. Within these systems beings live out a continuous stream of lives, on a constant wheel of birth, death and rebirth, in many different forms: human, animal, divine, ghostly and so on. Transmigration continues to occur so long as the individual remains attached to the notion that he or she has a permanent and unchanging self. Attachment to the idea of self causes suffering, a feeling that everything is not as it should be (dukkha), and each thought, action or desire must be worked out in a constant chain of cause and effect. The aim of Theravada practice is to escape from the wheel of rebirth and attain final liberation or nibbàna. Of the eighty two dhammas (the basic elements of existence) which are identified in the Theravàda Abhidhamma, nibbana is the only one which is unconditioned. Real progress towards this state is available only to monastics who have the opportunity to live according to the strict code of discipline and time to practice meditational techniques which lead to insight. The nature of nibbana cannot be described and questions about it are among the questions which the Buddha refused to answer on the grounds that it is beyond ordinary language and descriptions could not in any case be instrumental for salvation.      

The Theravada School is the only extant school of non-Mahayana Buddhism. Like other schools it traces its roots directly to the historical Buddha. Its predecessors, the Sthaviravadins divided off from the majority of the monks, the Mahasamghika, at around the time of the second Buddhist council at Vaisali (330-320 BCE), approximately one hundred years after the Buddha's death. The split may have been caused by differences in the understanding of the status of an arhat, but more likely by differences in the disciplinary code. The original Sthaviravadins were all monks of over ten years standing and therefore regarded as the elders of the community. The Sthaviravada school went on to divide further due in part to its geographical spread, but also because of developing disciplinary and doctrinal differences.
     In the third century BCE King Asoka led an attempt to purify the Sangha in India of aberrant or lax practices. According to Sri Lankan, Burmese and Thai Buddhist Chronicles,  Asoka was  responsible for sending missionary monks to these areas of South-East Asia, in around 247 BCE.
     The Theravada can be distinguished from other schools by its use of the Pali language for canonical literature. Theravada is the equivalent in Pali of Sthaviravada. The Pali scriptures were written down in Sri Lanka in the latter part of the first century BCE in response to economic and political circumstances including official support for non-Theravada teachings which threatened the Theravada claim to sole legitimacy. Commentaries to the canon were complete by the fifth century CE composed primarily by the Indian monk Buddhaghosa. The tradition has remained conservative with little further doctrinal development although the practice of Theravada Buddhism has been subject to decline and reform. On two occasions, after the Tamil invasion of Sri Lanka in the late tenth century and persecution led by a Saivite king in the sixteenth century, the ordination line was lost and subsequently reintroduced. The nuns' ordination line was lost completely in the tenth century.
     From the early centuries CE Theravada Buddhism was also introduced to parts of present day Thailand, Myanmar (Burma), Laos, Cambodia and Vietnam. In these areas Theravada teachings and practices reached accommodation with local belief systems and also with Mahayana and tantric elements of Buddhism. By the fourteenth and fifteenth centuries Buddhism in Thailand, Myanmar, Laos and Cambodia was mainly Sri Lankan Theravada. 

There are many symbols associated with Theravada Buddhism, for example the lotus which has its roots in the mud, representing samsara, but its buds and flowers in the clear air representing nirvana. The Buddha is often depicted seated on a lotus throne. A single footprint of Buddha also represents the presence of his teachings. Perhaps the most common symbol is the wheel or cakka often depicted with eight spokes representing the eight parts of the Noble Eightfold Path to enlightenment. 

Theravada Buddhism is now practised in Sri Lanka, Thailand, Myanmar, Laos, Cambodia and parts of India including Maharashtra. It is very difficult to estimate the numbers of adherents. In Myanmar and Thailand Buddhists form over eighty-five percent of the populations and in Sri Lanka, Cambodia, and Laos between seventy and eighty-five percent. There are probably about 400,000 Theravada monks distributed throughout these nations. Theravada Buddhism is one of several schools which have become popular in Western countries. Numbers of Western Buddhists are few in comparison with Asian populations but even so the interaction between Eastern and Western  Theravada Buddhists has been influential particularly in raising the status of the practice of the laity.

There are many centres of Theravada Buddhism including large numbers of monasteries. A useful organization of lay Theravàda Buddhists is the World Fellowship of Buddhists, which may be contacted at: 33 Sukhumvit Road, Between Soi 1 and Soi 2, Bangkok 10110, Thailand.