Florianópolis (Brazilian Portuguese: [floɾiaˈnɔpolis]; English: /ˌflɔːriæˈnɒpəlɪs/) is the capital and second largest city of the state of Santa Catarina, in the South region of Brazil. The city encompasses Santa Catarina Island and surrounding small islands, as well as part of the mainland. It has a population of 537,211, according to the 2022 Brazilian census, the second-most populous city in the state (after Joinville), and the 39th in Brazil. The metropolitan area has an estimated population of 1,111,702, the 21st largest in the country. The city is known for having the country's third-highest Human Development Index score among all Brazilian cities (0.847).

The economy of Florianópolis is heavily based on information technology, tourism, and services. The city has 60 beaches and is a center of surfing activity. Lagoa da Conceição is the most famous area for tourism, recreation, nature, and extreme sports. The New York Times reported that "Florianopolis is the party destination of the year in 2009." Newsweek placed Florianópolis in its "ten most dynamic cities of the world" list in 2006. Veja, a Brazilian publication, named the city as "the best place to live in Brazil." As a result of this exposure, Florianópolis is growing as a second home destination for many Paulistas, Argentines, Uruguayans, U.S. citizens, and Europeans.

Florianópolis is also commonly known by the nicknames Floripa and Ilha da Magia (Magic Island). Most of the population lives on the mainland and on the island's central and northern parts. The southern half is less inhabited. Many small commercial fishermen populate the island.

The Hercílio Luz International Airport serves the city. Florianópolis is home to the Universidade Federal de Santa Catarina (Federal University of Santa Catarina). There are also the Santa Catarina Federal Institute of Education, Science and Technology (Instituto Federal de Santa Catarina), and two campuses of the Universidade do Estado de Santa Catarina (State University of Santa Catarina), among other institutions of higher and professional education.

The city has been ranked as the safest capital to live in Brazil in 2024, according to the 2024 Security Atlas, released by the Institute for Applied Economic Research (IPEA) and the Brazilian Public Security Forum (FBSP). Among other rankings, it has been placed as well as the 5th best place to retire, in Brazil and the USA, by the Mongeral Aegon Longevity Institute in partnership with FGV.

The name Florianópolis is a tribute to Marshal Floriano Peixoto, the second President (1891–1894) of the Republic of the United States of Brazil and from Greek term polis, meaning "city". Until 1893, the city was called Nossa Senhora do Desterro (Portuguese: [ˈnɔsɐ siˈɲɔɾɐ du desˈteʁu] or [dʒisˈteʁu]; lit. 'Our Lady of Banishment') or simply Desterro.

Florianópolis lies within the Atlantic Forest, which has an extremely diverse and unique mix of vegetation and forest types. The main ecoregion is the coastal Atlantic forest, the narrow strip of about 50–100 kilometers (31–62 miles) along the coast, which covers about 20 percent of the region. This forest extends as far as 500–600 kilometers (310–370 miles) inland, and its range is as high as 2,000 meters above sea level. Altitude determines at least three vegetation types in the Atlantic Forest: the lowland forest of the coastal plain, montane forests, and the high-altitude grassland or "campo rupestre."

The municipality contains part of the 17,104-hectare (42,260-acre) offshore Marinha do Arvoredo Biological Reserve, a fully protected conservation unit established in 1990. It also contains part of the 84,130-hectare (207,900-acre) Serra do Tabuleiro State Park, a mountainous area covered in lush forests. The park protects the sources of the Vargem do Braço, Cubatão, and Una rivers, which supply most of the drinking water for greater Florianópolis and the south coast region. The municipality contains the 1,532-hectare (3,790-acre) Rio Vermelho State Park in the northeast of Santa Catarina Island, created in 2007.