Niterói is a municipality located in the state of Rio de Janeiro within the southeast region of Brazil. It sits across Guanabara Bay from the city of Rio de Janeiro and constitutes an integral part of the Rio de Janeiro Metropolitan Area. The city covers an area of 129.375 km² and had an estimated population of 515,317 inhabitants as of 2020, ranking it as the fifth most populous city in its state.
Historically, Niterói served as the capital of Rio de Janeiro from 1834 to 1894 and again from 1903 to 1975. It is known by the nickname Cidade Sorriso. The municipality is characterized by high social indicators; it held the highest Human Development Index in the state and the seventh highest among Brazil's municipalities in 2010. Additionally, it ranks as the municipality with the second highest average monthly household income per capita in Brazil.