The Pathet Lao (Lao ປະເທດລາວ, "Lao Nation") was a communist political movement and organization in Laos, formed in the mid-20th century. The group was ultimately successful in assuming political power after the Laotian Civil War. The Pathet Lao were always closely associated with Vietnamese communists. During the civil war, it was effectively organized, equipped and even led by the army of North Vietnam.

The Pathet Lao were the Laotian equivalent of North Vietnam's Vietnam People's Army, South Vietnam's Viet Minh and later Viet Cong, and Cambodia's Khmer Rouge. Eventually, the term became the generic name for Laotian communists.

The political movement of the Pathet Lao was called first the Lao People's Party (1955–1972) and later the Lao People's Revolutionary Party (1972–present).

Key Pathet Lao leaders include Prince Souphanouvong, Kaysone Phomvihane, Phoumi Vongvichit, Nouhak Phoumsavanh and Khamtay Siphandone.

The organization under this name first appeared in 1950, when it was adopted by Lao forces under Prince Souphanouvong, who joined the Viet Minh's revolt against the colonial French authorities in Indochina during the First Indochina War.

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.