Argentina, officially the Argentine Republic, is a country located mostly in the southern half of South America. Sharing the bulk of the Southern Cone with Chile to the west, the country is also bordered by Bolivia and Paraguay to the north, Brazil to the northeast, Uruguay and the South Atlantic Ocean to the east, and the Drake Passage to the south. With a mainland area of 2,780,400 km2 (1,073,500 sq mi), Argentina is the eighth-largest country in the world, the fourth largest in the Americas, the second largest in South America after Brazil, and the largest Spanish-speaking nation. The sovereign state is subdivided into twenty-three provinces and one autonomous city, Buenos Aires, which is the federal capital of the nation as decided by Congress. The provinces and the capital have their own constitutions, but exist under a federal system. Argentina claims sovereignty over part of Antarctica, the Falkland Islands (Islas Malvinas), and South Georgia and the South Sandwich Islands. The Inca Empire expanded to the northwest of the country in Pre-Columbian times. The country has its roots in Spanish colonization of the region during the 16th century.

Bolivia, officially the Plurinational State of Bolivia, is a landlocked country located in western-central South America. The constitutional capital is Sucre, while the seat of government and executive capital is La Paz. The largest city and principal industrial center is Santa Cruz de la Sierra. The sovereign state of Bolivia is a constitutionally unitary state, divided into nine departments. Its geography varies from the peaks of the Andes in the West, to the Eastern Lowlands, situated within the Amazon Basin. It is bordered to the north and east by Brazil, to the southeast by Paraguay, to the south by Argentina, to the southwest by Chile, and to the northwest by Peru. Bolivia is the fifth largest country in South America. The country's population, estimated at 11 million, is multiethnic, including Amerindians, Mestizos, Europeans, Asians and Africans. Spanish is the official and predominant language, although 36 indigenous languages also have official status, of which the most commonly spoken are Guarani, Aymara and Quechua languages.

Brazil, officially the Federative Republic of Brazil, is the largest country in both South America. Brazil is the world's fifth-largest country by area and the sixth most populous.Its capital is Brasília, and its most populous city is São Paulo. The federation is composed of the union of the 26 states and the Federal District. It is the largest country to have Portuguese as an official language and the only one in the Americas. It is also one of the most multicultural and ethnically diverse nations, due to over a century of mass immigration from around the world. It borders all other countries in South America except Ecuador and Chile. Its Amazon River basin includes a vast tropical forest, home to diverse wildlife, a variety of ecological systems, and extensive natural resources spanning numerous protected habitats. Brazil's current constitution, formulated in 1988, defines it as a democratic federal republic.

Chile, officially the Republic of Chile, is a country in western South America. It occupies a long, narrow strip of land between the Andes to the east and the Pacific Ocean to the west. Chile covers an area of 756,096 square kilometres (291,930 sq mi) and has a population of 17.5 million as of 2017. The capital and largest city is Santiago and the national language is Spanish. Chile borders Peru to the north, Bolivia to the northeast, Argentina to the east, and the Drake Passage in the far south. Chile is a high-income economy with high living standards. It is among South America's most economically and socially stable and prosperous nations.

Colombia, officially the Republic of Colombia, is a country largely in the north of South America, with territories in North America. Colombia is bounded on the north by the Caribbean Sea, the northwest by Panama, the south by Ecuador and Peru, the east by Venezuela, the southeast by Brazil, and the west by the Pacific. It comprises 32 departments and the Capital District of Bogotá, the country's largest city. Colombia is the fourth-largest country in South America. It is the world's third-most populous Spanish-speaking country. Its population is ethnically and linguistically diverse, with its rich multicultural heritage reflecting influences by several Amerindian civilizations, Spanish settlement, forced African labor, and immigration from Europe and the greater Middle East. Urban centres are concentrated in the Andean highlands and the Caribbean coast. Since 2005, there has been significant improvement in security, stability, and rule of law, as well as unprecedented economic growth and development. Colombia has the second-highest level of biodiversity in the world. Its territory encompasses Amazon rainforest, highlands, grasslands, and deserts, and it is the only country in South America with islands and coastlines along both the Atlantic and Pacific.

Ecuador, officially the Republic of Ecuador, is a country in northwestern South America, bordered by Colombia on the north, Peru on the east and south, and the Pacific Ocean on the west. Ecuador also includes the Galápagos Islands in the Pacific, about 1,000 kilometres (621 mi) west of the mainland. The capital and largest city is Quito. The legacy of both empires [Inca Empire and Spain] is reflected in Ecuador's ethnically diverse population, with most of its 17.1 million people being mestizos, followed by large minorities of European, Amerindian, and African descendants. Spanish is the official language and is spoken by a majority of the population, though 13 Amerindian languages are also recognized, including Quichua and Shuar. The sovereign state of Ecuador is a middle-income representative democratic republic and a developing country that is highly dependent on commodities, namely petroleum and agricultural products. It is governed as a democratic presidential republic. Ecuador hosts many endemic plants and animals. The new constitution of 2008 is the first in the world to recognize legally enforceable Rights of Nature, or ecosystem rights.

Guyana, officially the Co-operative Republic of Guyana, is a country on the northern mainland of South America. It is, however, often considered part of the Caribbean region because of its strong cultural, historical, and political ties with other Anglo-Caribbean countries. Guyana is bordered by the Atlantic Ocean to the north, Brazil to the south and southwest, Venezuela to the west, and Suriname to the east. With 215,000 square kilometres (83,000 sq mi), Guyana is the third-smallest sovereign state on mainland South America.  It gained independence in 1966, and officially became a republic within the Commonwealth of Nations in 1970. The legacy of British rule is reflected in the country's political administration and diverse population, which includes Indian, African, Amerindian, and multiracial groups. Guyana is the only South American nation in which English is the official language. The majority of the population, however, speak Guyanese Creole, an English-based creole language, as a first language.