São Luís (Brazilian Portuguese: [sɐ̃w luˈis], Saint Louis) is the capital and largest city of the Brazilian state of Maranhão. The city is located on Upaon-açu Island (Big Island, in Tupi Language) or Ilha de São Luís (Saint Louis' Island), in the Baía de São Marcos (Saint Mark's Bay), an extension of the Atlantic Ocean which forms the estuary of Pindaré, Mearim, Itapecuru and other rivers. Its coordinates are 2.53° south, 44.30° west. São Luís has the second largest maritime extension within Brazilian states. Its maritime extension is 640 km (397 miles). The city proper has a population of some 1,108,975 people (2020 IBGE estimate). The metropolitan area totals 1,605,305, ranked as the 15th largest in Brazil.

São Luís, created originally as Saint-Louis-de-Maragnan, is the only Brazilian state capital founded by France (see France Équinoxiale) and it is one of the three Brazilian state capitals located on islands (the others are Vitória and Florianópolis). The historic center of the city (dating from the 17th century) has its original street plan preserved and was named a UNESCO World Heritage Site in 1997.The city has two major sea ports: Madeira Port and Itaqui Port, through which a substantial part of Brazil's iron ore, originating from the (pre)-Amazon region, is exported. The city's main industries are metallurgical with Alumar, and Vale. São Luís is home of the Federal University of Maranhão.

São Luís was the home town of famous Brazilian samba singer Alcione, Brazilian writers Aluísio Azevedo, Ferreira Gullar and Josué Montello, Belgian-naturalised soccer player Luís Oliveira, and the musician João do Vale, a Música popular brasileira (MPB) singer.