The Co-tu have nearly 37,000 people inhabiting in Hien and Giang districts of Quang Nam-Da Nang province and A Luoi and Phu Loc districts of Thua Thien-Hue. Their other names are Gao, Ha, Phuong and Ca-tang. Co-tu language belongs to the Mon-Khmer Group. The Co-tu believe in Giang (Genie) and worship Giang.
Living in the Truong Son range, the Co-tu practice slash-and-burn cultivation and dig holes to put seeds in. Apart from rice, they practice animal husbandry, cloth weaving and basketry. Food gathering, hunting and fishing are also very common. The exchange of products is carried out by barter.
In the Co-tu village, the houses are set out in the form of an ellipse. In the middle of the village is the rong (communal house), a large and beautiful building which towers over all the other dwellings. This house is the place for reception of guests, to hold meetings, rituals and cultural performances. It is also here that the elders spend most of their time recounting their memories.
Co-tu attire is simple. Men wear loincloths and leave their upper torsos naked. Women wear skirts and short vests. In winter they wear a piece of cloth.
The popular ornaments comprise necklaces, bracelets and earrings. The traditional customs such as tattooing face and body, filing teeth and men wearing their hair long tied in a chignon have gradually declined.
Patriarchy prevails among the Co-tu. The children take the family name of the father. The right of inheritance is reserved for sons only. Each Co-tu lineage has its private name. Every one in each lineage must obey a certain taboo. Tales are written about the lineage's origin and its taboo. All people of a lineage are responsible for mutual help. The dead persons are buried tightly to one another in village burial ground. The Co-tu build funeral house on the grave and set many wood statues around it. Anniversaries of death or grave-cleaning do not exist among the Co-tu.
According to custom, cross-marriage between the two lineages are forbidden. If a man of A lineage marries a woman of B lineage, so man of this B is not allowed to marry woman of that A. He must find his wife from other lineages. If the husband died, the wife is allowed to get married his brother and vice versa. Marriage by purchase is a common practice. After the wedding, the bride comes to live in her husband's house. Monogamy is popular, but some rich people often take several wives.
Every year, the Co-tu hold big and small rituals worshipping genies to pray for good luck and health and especially bumper crops. The rituals are held mainly by each family and some big rites are held by whole people of the village, in particular the buffalo-stabbing rite.