All of the 13 independent nations of South America have written constitutions, and all are republics. Twelve of them have the presidential system of government, like that of the United States. Only Trinidad and Tobago has the parliamentary form of government, with a prime minister as head of government.

Three countries—Argentina, Brazil, and Venezuela—have federal systems. The others have centralized systems, being divided into departments or provinces for administrative purposes.

French Guiana is an overseas department of France; the Netherlands Antilles are an autonomous part of the Kingdom of the Netherlands; and the Falkland Islands are a territory of Great Britain.

Most South American countries' governments were overthrown by the military. Under these repressive regimes, citizens enjoyed few if any civil liberties. Beginning in the mid-1980's democratic civilian governments had returned to power in a few countries. By the mid-1990's all were governed by elected rulers.

Most South American countries have universal adult suffrage, and literacy requirements for voting have generally been eliminated. Poverty, geographic remoteness, and poor education keep people from voting in predominantly rural countries, but in others democratization has energized grassroots political activity.