Buddhism is the primary religion of Laos. The Buddhism practiced in Laos is of the Theravada tradition. Lao Buddhism is a unique version of Theravada Buddhism and is at the basis of Lao culture. Buddhism in Laos is often closely tied to animist beliefs and belief in ancestral spirits, particularly in rural areas.

The percentage of the population that adheres to Buddhism in modern Laos is variously reported, the CIA World Factbook estimates 65% of the total population have taken refuge in the Three Jewels. The creation of accurate estimates of the number of Buddhists in Laos is complicated by the paucity of information made available by the Laotian government, and the close connection between Buddhist and animist practices in Laos could make the numbers of nominal adherents of both Buddhism-Animism as much higher as over 90% because these traditions have influenced on mostly Lao people. It is still exclusive significant numbers of Chinese or Vietnamese Mahayana Buddhists.

Theravada Buddhism is believed to have first reached Laos during the 7th - 8th Centuries CE, via the kingdom of Dvaravati. During the 7th Century, tantric Buddhism was also introduced to Laos from the kingdom of Nan-chao, an ethnically Tai kingdom centered in modern day Yunnan, China. The Nan-chao kingdom also likely introduced the political ideology of the king as defender and protector of Buddhism, an important ideological tie between the monarchy and the sangha in much of Southeast Asia.

Laos ((ⁱ/ˈlaʊs/, /ˈlɑː.ɒs/, /ˈlɑː.oʊs/, or /ˈleɪ.ɒs/) Lao: ສາທາລະນະລັດ ປະຊາທິປະໄຕ ປະຊາຊົນລາວ, pronounced [sǎː.tʰáː.laʔ.naʔ.lat páʔ.sáː.tʰiʔ.páʔ.tàj páʔ.sáː.són.láːw] Sathalanalat Paxathipatai Paxaxon Lao), officially the Lao People's Democratic Republic, is a landlocked country in Southeast Asia, bordered by Burma and China to the northwest, Vietnam to the east, Cambodia to the south and Thailand to the west. Its population was estimated to be 6.5 million in 2012.

Laos traces its history to the Kingdom which existed from the 14th to the 18th century when it split into three separate kingdoms. In 1893, it became a French protectorate, with the three kingdoms, Luang Phrabang, Vientiane and Champasak, uniting to form what is now known as Laos. It briefly gained independence in 1945 after Japanese occupation, but returned to French rule until it was granted autonomy in 1949. Laos became independent in 1953, with a constitutional monarchy under Sisavang Vong. Shortly after independence, a long civil war ended the monarchy, when the Communist Pathet Lao movement came to power in 1975.

The Lao (Lao: ລາວ, Isan: ลาว, IPA: láːw) is an ethnic subgroup of Tai/Dai in Southeast Asia.

The etymology of the word Lao is uncertain, although it may be related to tribes known as the Ai Lao (Lao: ອ້າຽລາວ, Isan: อ้ายลาว, Chinese: 哀牢; pinyin: Āiláo, Vietnamese: ai lao) who appear in Han Dynasty records in China and Vietnam as a people of what is now Yunan Province. Tribes descended from the Ai Lao included the Tai tribes that migrated to Southeast Asia. The English word Laotian, used interchangeably with Lao in most contexts, comes from French laotien/laotienne. The Lao people, like many other Tai peoples also refer to themselves as Tai (Lao: ໄທ, Isan: ไท, IPA: tʰáj) and more specifically Tai Lao (ໄທລາວ, ไทลาว). In Thailand, the local Lao people are differentiated from the Lao of Laos and by the Thais by the term Thai Isan (Lao: ໄທຍ໌ອີສານ, Isan: ไทยอีสาน, IPA: i: să:n), a Sanskrit-derived term meaning northeast, but 'Lao' is still used.

According to a shared legend amongst various Tai tribes, a possibly mythical king, Khun Borom Rachathiriat (ຂຸນບໍຣົມຣາຊາທິຣາດ, ขุนบรมราชาธิราช, [kʰǔn bɔ̄ː lóm láː sáː tʰī lâːt]) of Mueang Thaen (ເມືອງແຖນ, เมืองแถน, [mɯ́əŋ tʰɛ̌ːn]) (modern-day Điện Biên Phủ) begot several sons that settled and ruled other mueang, or city-states, across South-East Asia and southern China. Descended from ancient peoples known to the Chinese as the Yue and the Ai Lao, the Tai tribes began migrating into South-East Asia by the beginning of the 1st millennium, but large-scale migrations took place between the 7th and 13th centuries AD, especially from what is now Sipsongbanna, Yunnan Province and Guangxi. The reasons for Tai migration include pressures from Han Chinese expansion, Mongol invasions, suitable land for wet rice cultivation and the fall of states such as Nanzhao that the Tais inhabited.