Porto Alegre (Portuguese pronunciation: [ˈpoɾtu aˈlɛɡɾi] ( listen), Happy Harbour) is the capital and largest city in the Brazilian state of Rio Grande do Sul. The city population is 1,509,939 inhabitants (2010), the tenth most populous city in the country and the centre of Brazil's fourth largest metropolitan area, with 4,018,482 inhabitants (2010). The city is the southernmost capital city of a Brazilian state. Porto Alegre is one of the top cultural, political and economic centers of Brazil. Two Mercosul countries, Argentina and Uruguay, border on the State of Rio Grande do Sul.

Porto Alegre was founded in 1772 by immigrants from the Azores, Portugal. In the late 19th century the city received many immigrants from other parts of the world, particularly Germany, Italy, and Poland. The vast majority of the population is of European descent.

The city lies on the eastern bank of the Rio Guaiba (Guaiba Lake), where five rivers converge to form the Lagoa dos Patos (Lagoon of the Ducks), a giant freshwater lagoon navigable by even the largest of ships. This five-river junction has become an important alluvial port as well as a chief industrial and commercial center of Brazil.