Niterói (Portuguese pronunciation: [niteˈɾɔj]) is a city and municipality in the state of Rio de Janeiro, in southeast region of Brazil. It has an estimated population of 487,327 inhabitants (2010) and an area of 129.375 km (80.39 mi)², being the sixth most populous city in the state and the highest Human Development Index Rio de Janeiro's city, and one of largest in Brazil. Integrates the Rio de Janeiro Metropolitan Area. The city has the nicknames of Niquiti, Nicki City and the Smile City (Cidade Sorriso).

Studies by the Getulio Vargas Foundation in June 2011 classified Niterói as the richest city of Brazil, with 55.7% of the population included in class A. Considering the classes A and B, Niterói also appears in the first place, with 85.9% of the population entered in these classes. The word "Niterói" comes from the Tupi language and means "water that hides".

This city was founded on November 22, 1573 by the Tupi Amerindian chief Araribóia (who later was converted to Roman Catholicism and given the Christian name of Martim Afonso, after the Portuguese explorer Martim Afonso de Sousa). It makes Niteroi the only Brazilian city to have been founded by a non-Christian, non-assimilated Brazilian Amerindian..