Floreana Island (Spanish: Isla Floreana) is a southern island in Ecuador's Galápagos Archipelago. The island has an area of 173 km (67 sq mi). It was formed by volcanic eruption. The island's highest point is Cerro Pajas at 640 m (2,100 ft), which is also the highest point of the volcano like most of the smaller islands of Galápagos. The island has a population of about 100.

Floreana, sometimes written as Floriana, is named in honor of Juan José Flores, the first president of Ecuador. It was during Flores's presidency that Ecuador took possession of the archipelago. The island was previously known in Spanish as Mercedes Island (Isla Mercedes), sometimes corrupted to Mascarenas, in honor of Flores's wife Mercedes Jijón. It was also known as Santa Maria, after the Virgin Mary and the Santa María, one of Christopher Columbus's ships during his initial voyage. Pinta Island similarly remembers another one of his ships.

The English pirate William Ambrosia Cowley did not apparently chart or name this island in his 17th-century accounts of the Galápagos but the British captain James Colnett misunderstood some of Cowley's maps and in 1793 gave Floreana the name King Charles and Charles Island, which Cowley had given to Española Island in honor of King Charles II of England. (He similarly named Santiago after James II.) When it is used, the name Charles Island is still applied following Colnett's misplacement rather than Cowley's original intention.

Due to its relatively flat surface, supply of fresh water as well as plants and animals, Floreana was a favorite stop for whalers and other visitors to the Galápagos. Since the 19th century, whalers kept a wooden barrel at Post Office Bay, so that mail could be picked up and delivered to their destination by ships on their way home, mainly to Europe and the United States. Cards and letters are still placed in the barrel without any postage. Visitors sift through the letters and cards in order to deliver them by hand.

Still known as Charles Island, the island was set afire in 1820 as a result of a prank gone wrong by helmsman Thomas Chappel from the Nantucket whaling ship Essex. Being at the height of the dry season, Chappel's fire soon burned out of control and swept the island. The next day saw the island still burning as the ship sailed for an offshore anchorage and after a full day of sailing the fire was still visible on the horizon. Many years later Thomas Nickerson, who had been a cabin boy on the Essex, returned to Charles Island and found a black wasteland: "neither trees, shrubbery, nor grass have since appeared." It is believed the fire contributed to the extinction of some species originally on the island.

In September 1835 the second voyage of HMS Beagle brought Charles Darwin to Charles Island. The ship's crew was greeted by Nicholas Lawson, acting for the Governor of Galápagos, and at the prison colony Darwin was told that tortoises differed in the shape of the shells from island to island, but this was not obvious on the islands he visited and he did not bother collecting their shells. He industriously collected all the animals and plants, and speculated about finding "from future comparison to what district or 'centre of creation' the organized beings of this archipelago must be attached."

On 8 April 1888 USS Albatross, a Navy-manned research vessel assigned to the United States Fish Commission visited Floreana Island during a 2-week survey of the islands.

In 1929, Friedrich Ritter and Dore Strauch arrived in Guayaquil from Berlin to settle on Floreana and sent letters back that were widely reported in the press, encouraging others to follow. In 1932, Heinz and Margret Wittmer arrived with their son Harry from Germany, and shortly afterwards their son Rolf was born there, the first person known to have been born in the Galápagos. Later in 1932, the Austrian "Baroness" von Wagner Bosquet arrived with two German companions, Robert Philippson and Rudolph Lorenz, as well as the Ecuadorian guide Manuel Valdivieso Borja. A series of strange disappearances and deaths (including possible murders) and the departure of Strauch then left the Wittmers as the sole remaining inhabitants of the group who had settled there. They set up a hotel which is still managed by their descendants. Mrs. Wittmer wrote an account of her experiences as Floreana: A Woman's Pilgrimage to the Galápagos. While residing in Tahiti in 1935, Georges Simenon wrote the novel Ceux de la Soif, which recounts these events in fictionalized form. The story was first published as a feuilleton in the newspaper Le Soir between 12 December 1936 and 1 January 1937, and as a novel by Gallimard in 1938. Simenon´s novel was adapted for television in 1989, by Laurent Heynemann. A documentary film recounting these events, The Galapagos Affair, was released in 2013. A fictionalized film by director Ron Howard starring Jude Law, Sydney Sweeney, and Ana de Armas premiered at the Toronto Film Festival in 2024.

Asilo de la Paz, located in the highlands of Floreana Island, was the site of the island's first human settlement and is now among its most popular tourist attractions.

The demands of these visitors, early settlers, and introduced species devastated much of the local wildlife with the endemic Floreana tortoise being declared extinct and the endemic Floreana mockingbird becoming extirpated on the island (the few remaining are found on the nearby islands of Gardiner and Champion).

Floreana is a shield volcano, which has erupted alkaline basalts since 1.5 Ma. It is the southernmost island in the Galapagos Archipelago, and a 3,400 m submarine escarpment 10 km south of the island forms the southern boundary of the Galapagos Platform. There are over 50 scoria cones onshore and 6 tuff cones offshore. Mostly composed of tephra, these cones are the origin of the A'a lava flows. The oldest flows are on the northern end of the island, while the youngest (26 ka) are on the southern end. Cerro Pajas, the tallest inactive volcano on the island, is the origin of the largest lava flow (272 ka).

The island has been recognised as an Important Bird Area (IBA) by BirdLife International. It supports one of the main colonies of critically endangered Galápagos petrels in the archipelago, with about 350 nests scattered beneath a dense vegetation among the rocks. Medium tree finches are endemic to the island. Other significant species include lava gulls, Galapagos penguins, and at one point in time the locally extinct Floreana mockingbird.

When Charles Darwin visited the island in 1835, he found no sign of its native tortoise and assumed that whalers, pirates, and human settlers had wiped them out. Since about 1850, no tortoises have been found on the island (except for one or two introduced animals kept as pets by the locals), and the International Union for Conservation of Nature classified the Floreana giant tortoise (Chelonoidis elephantopus sometimes called Chelonoidis nigra) as extinct. However, it may be that there are pure Floreana tortoises living on other islands in the archipelago.

• A favorite dive and snorkeling site, “Devil's Crown”, located off the northeast point of the island, is an underwater volcanic cone, offering the opportunity to snorkel with schools of fish, sea turtles, sharks and sea lions, which are abundant amongst the many coral formations found here.
• At Punta Cormorant, there is a green olivine beach to see sea lions and a short walk past a lagoon to see flamingos, rays, sea turtles, and Grapsus grapsus (Sally Lightfoot) crabs. Pink flamingos and green sea turtles nest from December to May on this island. The "joint footed" petrel is found here, a nocturnal sea bird which spends most of its life away from land.
• Post Office Bay provides visitors the opportunity to send post cards home without a stamp via the over 200-year-old post barrel and other travelers.
• A miniature football field, complete with goals, at the end of Post Office Bay, is used by tour boat crews and their tourists.

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  Floreana Island
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  Post Barrel
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  Punta Cormorant with American flamingos

• Floreana at Galapagos Online