Rio de Janeiro is the second largest city of Brazil and South America, behind São Paulo, and the third largest metropolitan area in South America, behind São Paulo and Buenos Aires. The city is capital of the state of Rio de Janeiro. It was the capital of Brazil for almost two centuries, from 1763 to 1822 while it was a Portuguese colony and from 1822 to 1960 as an independent nation. It was the capital of the Portuguese Empire from 1808 to 1821. Commonly known as just Rio, the city is also nicknamed A Cidade Maravilhosa, or "The Marvelous City".

Rio de Janeiro is famous for its natural settings, its Carnival celebrations, samba and other music, and hotel-lined tourist beaches, such as Copacabana and Ipanema, paved with decorated black and cream swirl pattern mosaics known locally as "pedra portuguesa". Some of the most famous local landmarks in addition to the beaches include the giant statue of Jesus, known as Christ the Redeemer ('Cristo Redentor') atop Corcovado mountain, which has recently been named one of the New Seven Wonders of the World; Sugarloaf mountain (Pão de Açúcar) with its cable car; the Sambódromo, a giant permanent parade stand used during Carnival and Maracanã stadium, one of the world's largest football stadiums.

The city also boasts the largest and second largest urban forests in the world: Floresta da Tijuca, or "Tijuca Forest". and (almost connected to the first) the forest in Parque Estadual da Pedra Branca, or White Stone State Park. Galeão - Antônio Carlos Jobim International Airport connects Rio de Janeiro with many Brazilian cities and also operates several international flights.

Despite its charm and beauty, Rio is reputed to be one of the most violent cities in the world and motivated movies such as Bus 174, City of God and Elite Squad portraying severe social issues. Much of the violent crime is concentrated in the "favelas," or shantytowns. But it also spills into middle- and upper-income neighborhoods. In Rio, unlike other major cities, many of the slums are directly adjacent to some of the wealthiest areas of the city.

Rio de Janeiro is located at 22 degrees, 54 minutes south latitude, 43 degrees 14 minutes west longitude. The population of the City of Rio de Janeiro is about 6,136,652, occupying an area of 1,182.3 square kilometres (456.5 sq mi).

The population of the larger metropolitan area is estimated at 11-13.5 million. It was Brazil's capital until 1960, when Brasília took its place. Residents of the city are known as Cariocas. The official song of Rio is "Cidade Maravilhosa" (translated as "Marvelous City").

Rio has a tropical climate. The temperature occasionally reaches over 40°C (104°F) in inland areas of the city, and extreme maximum temperatures above 30°C (86°F) can happen every month. In the main tourist areas (south side, where the beaches are located), the temperature is moderated by the cool sea-breezes from the ocean.

The average annual minimum temperature is 20°C (68°F), the average annual maximum temperature is 26°C (79°F) and the average annual temperature is 23°C (73.5°F). The average yearly precipitation is 1,086 mm. The minimum temperature recorded was 4.8°C (40°F) in July 1928, but temperatures below 10°C (50°F) are rare in most of city today, the absolute maximum reached 43.2°C (110°F) in January 1984.

Centro (Downtown in American English or CBD in other English use) is the historic centre of the city, as well as its financial centre. Sites of interest include the Paço Imperial, built during colonial times to serve as a residence for the Portuguese governors of Brazil; many historic churches, such as the Candelária Church, the colonial Cathedral and the modern-style Rio de Janeiro Cathedral. Around the Cinelândia square there are several landmarks of the Belle Époque of Rio, such as the Municipal Theatre and the National Library building. Among its several museums, the Museu Nacional de Belas Artes (National Museum of Fine Arts) and the Museu Histórico Nacional (National Historical Museum) are the most important. Other important historical attractions in central Rio include its Passeio Público, an 18th-century public garden, as well as the imposing arches of the Arcos da Lapa, a Roman-style aqueduct built around 1750. A bondinho (tram) leaves from a city center station, crosses the aqueduct (converted to a tram viaduct in 1896) and rambles through the hilly streets of the Santa Teresa neighbourhood nearby.

Downtown remains the heart of the city's business community. Some of the largest companies in Brazil have their head offices here, including Petrobras and Vale (formerly Companhia Vale do Rio Doce), the two largest Brazilian corporations.

The Brazilian carnival (Carnaval, in Portuguese) is an annual celebration held 40 days before Easter and marking the beginning of Lent. Rio de Janeiro has many Carnival choices, including the famous Samba school (Escolas de Samba) parades in the sambadrome exhibition centre and the popular blocos de carnaval, which parade in almost every corner of the city. The most famous ones are:

* Cordão do Bola Preta: Parades in the centre of the city. It is one of the most traditional carnavals. In 2008, 500,000 people attended in one day.
* Suvaco do Cristo: Band that parades in the Botanic Garden, directly below the Redeemer statue's arm. The name, in English, translates as 'Christ's armpit', and was chosen for that reason.
* Carmelitas: Band that was supposedly created by nuns, but in fact it is just a theme chosen by the band. It parades in the hills of Santa Teresa, which have very nice views.
* Simpatia é Quase Amor: One of the most popular parades in Ipanema. Translates as 'Friendliness is almost love'.
* Banda de Ipanema: The most traditional in Ipanema. It attracts a wide range of revellers, including families and a wide spectrum of the gay population (notably spectacular drag queens).

In 1840, the first Carnaval was celebrated with a masked ball. As years passed, adorned floats and costumed revelers became a tradition amongst the celebrants. Carnaval is known as a historic root of Brazilian music.

Apart from Carnaval, New Year is also a major event in Rio. It's celebrated with concerts and firework displays all around Rio, the largest one being in Copacabana beach. People wear white clothes, and some of them make offerings to Iemanjá, a deity in many of the Afro-Brazilian religions (e.g. Candomble, Umbanda, Macumba).

There are several significant museums in Rio as well. Among them are the Quinta da Boa Vista (which includes the National Museum of Brazil), the Native Art Museum (primitives, with the largest collection of native paintings in the world), and the Indian Museum.

Rio has an extensive nightlife scene. Clubs like Baronneti, Nuth, and Catwalk are some of the country's best known and frequented by celebrities such as Ronaldo, Calvin Klein, Mick Jagger, and Naomi Campbell.