Ethnic, religious, and linguistic distinctions in Sri Lanka are essentially the same. Three ethnic groups—Sinhalese, Tamil, and Muslim—make up more than 99 percent of the country's population, with the Sinhalese alone accounting for nearly three-fourths of the people. The Tamil segment comprises two groups—Sri Lankan Tamils (long-settled descendants from southeastern India) and Indian Tamils (recent immigrants from southeastern India, most of whom were migrant workers brought to Sri Lanka under British rule). Slightly more than one-eighth of the total population belongs to the former group. Muslims, who trace their origin back to Arab traders of the 8th century, account for about 7.5 percent of the population. Burghers (a community of mixed European descent), Parsis (immigrants from western India), and Veddas (regarded as the aboriginal inhabitants of the country) total less than 1 percent of the population.

The Sinhalese constitute the majority in the southern, western, central, and north-central parts of the country. In the rural areas of the Wet Zone lowlands, they account for more than 95 percent of the population. The foremost concentration of the Sri Lankan Tamils lies in the Jaffna Peninsula and in the adjacent districts of the northern lowlands. Smaller agglomerations of this group are also found along the eastern littoral where their settlements are juxtaposed with those of the Muslims. The main Muslim concentrations occur in the eastern lowlands. In other areas, such as Colombo, Kandy, Puttalam, and Gampaha, Muslims form a small but important segment of the urban and suburban population. The Indian Tamils, the vast majority of whom are plantation workers, live in large numbers in the higher areas of the Central Highlands.