The Maasai have a number of patrilineal clans grouped into two classes, or moieties. The basic institution of social integration, however, is the system of age-sets. Under this system, groups of the same age are initiated (circumcised) into adult life during the same open-initiation period; the age-class thus formed is a permanent grouping, lasting the life of its members. They move up through a hierarchy of grades, each lasting approximately 15 years, including those of junior warriors, senior warriors, and junior elders, until they become senior elders authorized to make decisions for the tribe. Maasai society is remarkably egalitarian; slaves have never been kept.

Between the ages of about 14 and 30, young men are traditionally known as morans. During this life stage they live in isolation in the bush, learning tribal customs and developing strength, courage, and endurance—traits for which Maasai warriors are noted throughout the world.

Ceremonial events are directed by a ritual expert (oloiboni) who, although he has no political power, is religious head of his people.

The Kenyan and Tanzanian governments are encouraging the Maasai to make permanent agricultural settlements and to give up the practice of isolating young men, in favour of formal education and greater assimilation.