Rio de Janeiro (/ˈriːoʊ di ʒəˈnɛəroʊ, -deɪ ʒə-, -də dʒə-/; Portuguese pronunciation: [ˈʁi.u dʒi ʒɐˈnejɾu];River of January), or simply Rio, is the second-largest city in Brazil, the sixth-largest city in the Americas, and the world's thirty-ninth largest city by population. The metropolis is anchor to the Rio de Janeiro metropolitan area, the second most populous metropolitan area in Brazil, the seventh-most populous in the Americas, and the twenty-third largest in the world. Rio de Janeiro is the capital of the state of Rio de Janeiro, Brazil's third-most populous state. Part of the city has been designated as a World Heritage Site, named "Rio de Janeiro: Carioca Landscapes between the Mountain and the Sea", by UNESCO on 1 July 2012 as a Cultural Landscape.

Founded in 1565 by the Portuguese, the city was initially the seat of the Captaincy of Rio de Janeiro, a domain of the Portuguese Empire. Later, in 1763, it became the capital of the State of Brazil, a state of the Portuguese Empire. In 1808, when the Portuguese Royal Court transferred itself from Portugal to Brazil, Rio de Janeiro became the chosen seat of the court of Queen Maria I of Portugal, who subsequently, in 1815, under the leadership of her son, the Prince Regent, and future King João VI of Portugal, raised Brazil to the dignity of a kingdom, within the United Kingdom of Portugal, Brazil, and Algarves. Rio stayed the capital of the pluricontinental Lusitanian monarchy until 1822, when the War of Brazilian Independence began. This is one of the few instances in history that the capital of a colonising country officially shifted to a city in one of its colonies. Rio de Janeiro subsequently served as the capital of the independent monarchy, the Empire of Brazil, until 1889, and then the capital of a republican Brazil until 1960 when the capital was transferred to Brasília.

The 2016 Summer Olympics (Portuguese: Jogos Olímpicos de Verão de 2016), officially known as the Games of the XXXI Olympiad, and commonly known as Rio 2016, are a major international multi-sport event that will take place in Rio de Janeiro, Brazil, from August 5 to August 21, 2016. Record numbers of countries and sets of medals are awaiting in the games. More than 10,500 athletes from 206 National Olympic Committees (NOCs), including from Kosovo and South Sudan for the first time, will take part in this sporting event. With 306 sets of medals, the games will feature 28 Olympic sports — including rugby sevens and golf, which were added by the International Olympic Committee in 2009. These sporting events will take place on 33 venues in the host city and additionally on 5 venues in the cities of São Paulo (Brazil's largest city), Belo Horizonte, Salvador, Brasília (Brazil's capital), and Manaus.

The host city of Rio de Janeiro was announced at the 121st IOC Session held in Copenhagen, Denmark, on 2 October 2009. The other finalists were Madrid, Spain; Chicago, United States; and Tokyo, Japan. Rio will become the first South American city to host the Summer Olympics, the second city in Latin America to host the event after Mexico City in 1968, and the first since 2000 in the Southern Hemisphere. This will be the third time the Summer Olympics are held in a developing country, after the 1968 Games in Mexico and the 1988 Games in South Korea.

Rio de Janeiro (Portuguese pronunciation: [ˈʁi.u dʒi ʒɐˈnejɾu]) is one of the 27 states of Brazil. It has the second largest economy of Brazil, with the largest being that of the state of São Paulo.

The state of Rio de Janeiro is located within the Brazilian geopolitical region classified as the Southeast (assigned by IBGE). Rio de Janeiro shares borders with all the other states in the same Southeast macroregion: Minas Gerais (N and NW), Espírito Santo (NE) and São Paulo (SW). It is bounded on the east and south by the Atlantic Ocean. Rio de Janeiro has an area of 43,653 km². Its capital is the city of Rio de Janeiro, which was the capital of the Portuguese Colony of Brazil from 1763 to 1815, of the United Kingdom of Portugal, Brazil and the Algarves from 1815 to 1822, and of independent Brazil from 1822 to 1960.

The 20 state's largest cities are Rio de Janeiro, São Gonçalo, Duque de Caxias, Nova Iguaçu, Niterói, Campos dos Goytacazes, Belford Roxo, São João de Meriti, Petrópolis, Volta Redonda, Magé, Macaé, Itaboraí, Cabo Frio, Angra dos Reis, Nova Friburgo, Barra Mansa, Teresópolis, Mesquita and Nilópolis.