Theravāda also includes a rich diversity of traditions and practices that have developed over its long history of interactions with varying cultures and religious communities. It is the dominant form of religion in Cambodia, Laos, Myanmar, Sri Lanka, and Thailand, and is practiced by minority groups in India, Bangladesh, China, Nepal, and Vietnam. In addition, the diaspora of all of these groups as well as converts around the world practice Theravāda Buddhism. Contemporary expressions include Buddhist modernism, the Vipassana movement and the Thai Forest Tradition.
Theravāda Buddhism is followed by countries and people around the globe, and is:
Today, Theravāda Buddhists, otherwise known as Theravadins, number over 150 million worldwide, and during the past few decades Theravāda Buddhism has begun to take root in the West and in the Buddhist revival in India.
The name Theravāda comes from the ancestral Sthāvirīya, one of the early Buddhist schools, from which the Theravadins claim descent. After unsuccessfully trying to modify the Vinaya, a small group of "elderly members", i.e. sthaviras, broke away from the majority Mahāsāṃghika during the Second Buddhist council, giving rise to the Sthavira sect. According to its own accounts, the Theravāda school is fundamentally derived from the Vibhajjavāda "doctrine of analysis" grouping, which was a division of the Sthāvirīya.
Buddhists from the Indian mainland appear originally to have regarded the Buddhists of Laṅkā as simply the 'Laṅkā school', thus Vasubandhu writing in the fourth century cites the notion of the bhavāṅga-vijñāna of the Tāmraparṇīya-nikāya as a forerunner of the ālaya-vijñāna. But beginning with Yijing's account of his travels in India (671–695 CE) and Vinītadeva's eighth-century summary of the divisions of the Buddhist schools (Samaya-bhedoparacana- cakra-nikāya-bhedopadarśana-cakra), we find north Indian sources describing the Buddhist Saṅgha as comprising four nikāyas: (1) the Mahāsāṃghikas, (2) the Sthāviras, (3) the Sarvāstivādins, and (4) the Saṃmatīyas. Significantly, the Sthāviras in turn comprise three sub-nikāyas: the Jetavanīyas, the Abhayagirivāsins, and the Mahāvihāravāsins. The Buddhists of Laṅkā are thus no longer regarded as the ‘Laṅkā school’, they are the Sthāviras, despite the fact that both the Sarvāstivādins and the Saṃmatīyas were also understood as tracing their lineage to the Sthāvira side of the original split with the Mahāsāṃghikas. The reason for referring to the three Buddhist nikāyas of Laṅkā as the Sthāviras is probably not so much a recognition of an exclusive claim to be the authentic theravāda, as a reflection of the simple fact that the Laṅkā schools alone of the various Sthāvira schools continued to refer to themselves as theriya or theravāda in certain contexts.