The so-called Lao Loum (or lowland Lao) live at the lowest elevations and on the land best suited for cultivation. For the most part, they are the ethnic Lao , a people related to the Thai of Thailand and the Shan of Burma. The lowland Lao make up the majority in Laos, between 50 percent and 60 percent. They prefer to inhabit river valleys and practise Theravada Buddhism as well as some animist rituals. Of all the ethnicities found in Laos, the culture of the lowland Lao is dominant, mainly because it is they who hold political power. Their language is the official language, their religion is the state religion and their holy days are the official holidays.

Akin to the ethnic Lao are the Tai Leu , Phuan and Phu Tai , found in the northwest, the northeast and mid-south respectively. They are all Theravada Buddhists and, like the Lao, also placate animist spirits. Most have assimilated into Lao culture.

Other Tai peoples related to the Lao are the so-called " tribal Tai ", who are mostly animists. These include the Tai Daeng (Red Tai), Tai Khao (White Tai) and Tai Dam (Black Tai). Tai Dam women wear long-sleeved, tight-fitting blouses in bright colours with a row of butterfly-shaped silver buttons down the front plus a long, indigo-coloured skirt and an indigo bonnet.