In course of time, the Garos society was divided into three major exogamous, 'Kin-groups' or Chachis, namely Sangma, Marak and Momin. These are further sub-divided into such groups as Areng, Shira and Ebang.

Marriage between members of the same Chachi is totally prohibited by tribal law. Each of these Kin-groups is further sub-divided into a number of lineages called Machong. The Machong with its component households is the basic unit in the Garo social organization. A Garo belong to his particular Machong from his birth. In each village, the dominant Machong selects the headman who is Nok-ma literally means house-mother. Usually Nok-ma would be a man.

Inheritance among the Garos is restricted to the female line. Each family selects an heiress (Nok`na). A couple with no children may adopt the daughter of the wife's sister as heiress. The heiress is usually linked in marriage with the son of the father's sister.

The institution of the 'Bachelors Dormitory' (Nokpante) is found only among the Garos. All unmarried young men and growing boys must live in the dormitory. These young people carry out allotted tasks entrusted to them by the village elders.

The Garo tribal group consists of sub-tribes. They are

(a) Ambeng (in the western part including Tura)
(b) Atong (in the lower Simsang valley)
(c) Akawe (north-eastern parts and extend upto Goalpara and Kamrup in Assam)
(d) Matchi (upper reaches of Simsang valley)
(e) Chibok (upper Bhugi valley)
(f) Ruga (lower Bhugi valley)
(g) Dual (upper Simsang valley)
(h) Chisak (north of Matchi and Dual in central highlands)
(j) Kotchu (eastern parts)
(k) Koch (south-western parts)


Besides these, there are others like Megamo in the mid-western parts and the Dikos.