Sinhalese make up 74% of the population and are concentrated in the densely populated southwest. Ceylon Tamils, citizens whose South Indian ancestors have lived on the island for centuries, total about 12% and live predominantly in the north and east.

Indian Tamils, a distinct ethnic group, represent about 5% of the population. The British brought them to Sri Lanka in the 19th century as tea and rubber plantation workers, and they remain concentrated in the "tea country" of south-central Sri Lanka. In accordance with a 1964 agreement with India, Sri Lanka granted citizenship to 230,000 "stateless" Indian Tamils in 1988. Under the pact, India granted citizenship to the remainder, some 200,000 of whom now live in India. Another 75,000 Indian Tamils, who themselves or whose parents once applied for Indian citizenship, now wish to remain in Sri Lanka. The government has stated these Tamils will not be forced to return to India, although they are not technically citizens of Sri Lanka. In October of 2003, an act of Parliament granted citizenship to several thousand of these ìtea estateî Tamils.

Other minorities include Muslims (both Moors and Malays), at about 7% of the population; Burghers, who are descendants of European colonists, principally from the Netherlands and the United Kingdom (U.K.); and aboriginal Veddahs. Most Sinhalese are Buddhist; most Tamils are Hindu. The majority of Sri Lanka's Muslims practice Sunni Islam. Sizable minorities of both Sinhalese and Tamils are Christians, most of whom are Roman Catholic. The 1978 constitution, while assuring freedom of religion, grants primacy to Buddhism.

Sinhala, an Indo-European language, is the native tongue of the Sinhalese. Tamils and most Muslims speak Tamil, part of the South Indian Dravidian linguistic group. Use of English has declined since independence, but it continues to be spoken by many in the middle and upper middle classes, particularly in Colombo. The government is seeking to reverse the decline in the use of English, mainly for economic but also for political reasons. Both Sinhala and Tamil are official languages.