The Galápagos Islands (Spanish: Islas Galápagos) are an archipelago of volcanic islands in the Eastern Pacific, located around the equator, 900 km (560 mi) west of the mainland of South America. They form the Galápagos Province of the Republic of Ecuador, with a population of slightly over 33,000 (2020). The province is divided into the cantons of San Cristóbal, Santa Cruz, and Isabela, the three most populated islands in the chain. The Galápagos are famous for their large number of endemic species, which were studied by Charles Darwin in the 1830s and inspired his theory of evolution by means of natural selection. All of these islands are protected as part of Ecuador's Galápagos National Park and Marine Reserve.

There is no firm evidence that Polynesians or the Indigenous peoples of South America reached the islands before their accidental discovery by Bishop Tomás de Berlanga in 1535. If some visitors did arrive, poor access to fresh water on the islands seems to have limited settlement. The Spanish Empire similarly ignored the islands, although during the Golden Age of Piracy various pirates used the Galápagos as a base for raiding Spanish shipping along the Peruvian coast. The goats and black and brown rats introduced during this period greatly damaged the existing ecosystems of several islands. British sailors were chiefly responsible for exploring and mapping the area. Darwin's voyage on HMS Beagle was part of an extensive British survey of the coasts of South America. Ecuador, which won its independence from Spain in 1822 and left Gran Colombia in 1830, formally occupied and claimed the islands on 12 February 1832 while the voyage was ongoing. José de Villamil, the founder of the Ecuadorian Navy, led the push to colonize and settle the islands, gradually supplanting the English names of the major islands with Spanish ones. The United States built the islands' first airport as a base to protect the western approaches of the Panama Canal in the 1930s. After World War II, its facilities were transferred to Ecuador. With the growing importance of ecotourism to the local economy, the airport modernized in the 2010s, using recycled materials for any expansion and shifting entirely to renewable energy sources to handle its roughly 300,000 visitors each year.

The Galápagos or Galapagos Islands are named for their giant tortoises, which were more plentiful at the time of their discovery. The Spanish word galápago derives from a pre-Roman Iberian word meaning "turtle", the meaning it still has in most dialects. Within Ecuadorian Spanish, however, it is now also used to describe the islands' large tortoises. It is usually read /ɡəˈlæpəɡəs/ in British English and /ɡəˈlɑːpəɡəs/ in American English. The name is first attested as the Spanish/Latin hybrid Insulae de los Galopegos ("Islands of the Turtles") on the map of the Americas in Abraham Ortelius's Theater of the Lands of the World (Theatrum Orbis Terrarum), first published in 1570.

The islands were also previously known as the Enchanted Isles or Islands (Islas Encantadas) from sailors' difficulty with the winds and currents around them; as the Ecuador Archipelago (Archipiélago de Ecuador) or Archipelago of the Equator (Archipiélago del Ecuador) following their settlement by Ecuador in 1832; and as the Colon or Columbus Archipelago (Archipiélago del Colón) in 1892 upon the quadricentennial of Columbus's first voyage.

The islands were mapped by the English buccaneer William Ambrosia Cowley in 1684 and by the British captain James Colnett in 1793. The names they chose to honour British kings, nobles, and naval officers of their eras continued to be used for the major islands until recently and are still used for many of the smaller islets. The Spanish names have varied over time, but the current official names have gradually supplanted the English ones for most of the major islands.

Volcanism has been continuous on the Galápagos Islands for at least 20 million years, and perhaps even longer. The mantle plume beneath the eastward-moving Nazca plate (51 km/Myr) has given rise to a 3-kilometre-thick platform under the island chain and seamounts. Besides the Galápagos Archipelago, other key tectonic features in the region include the Northern Galápagos volcanic province between the archipelago and the Galápagos Spreading Center (GSC) 200 km (120 mi) to the north at the boundary of the Nazca plate and the Cocos plate. This spreading center truncates into the East Pacific Rise on the west and is bounded by the Cocos Ridge and Carnegie Ridge in the east. Furthermore, the Galápagos Hotspot is at the northern boundary of the Pacific Large Low Shear Velocity Province while the Easter Hotspot is on the southern boundary.

The Galápagos Archipelago is characterized by numerous contemporaneous volcanoes, some with plume magma sources, others from the asthenosphere, possibly due to the young and thin oceanic crust. The GSC caused structural weaknesses in this thin lithosphere leading to eruptions forming the Galápagos Platform. Fernandina and Isabela in particular are aligned along these weaknesses. Lacking a well-defined rift zone, the islands have a high rate of inflation prior to eruption. Sierra Negra on Isabela Island experienced a 240 cm (94 in) uplift between 1992 and 1998, most recent eruption in 2005, while Fernandina on Fernandina Island indicated an uplift of 90 cm (35 in), most recent eruption in 2009. Alcedo on Isabela Island had an uplift of greater than 90 cm, most recent eruption in 1993. Additional characteristics of the Galápagos Archipelago are closer volcano spacing, smaller volcano sizes, and larger calderas. For instance, Isabela Island includes six major volcanoes, Ecuador, Wolf, Darwin, Alcedo, Sierra Negra and Cerro Azul, with most recent eruptions ranging from 1813 to 2008. The neighboring islands of Santiago and Fernandina last erupted in 1906 and 2009, respectively. Overall, the nine active volcanoes in the archipelago have erupted 24 times between 1961 and 2011. The shape of these volcanoes is tall and rounded as opposed to wide and smooth in the Hawaiian Islands. The Galápagos's shape is due to the pattern of radial and circumferential fissure, radial on the flanks, but circumferential near the caldera summits. It is the circumferential fissures which give rise to stacks of short lava flows.

The volcanoes at the west end of the archipelago are in general, taller, younger, have well-developed calderas, and are mostly composed of tholeiitic basalt, while those on the east are shorter, older, lack calderas, and have a more diverse composition. The ages of the islands, from west to east are 0.05 Ma for Fernandina, 0.65 Ma for Isabela, 1.10 Ma for Santiago, 1.7 Ma for Santa Cruz, 2.90 Ma for Santa Fe, and 3.2 Ma for San Cristobal. The calderas on Sierra Negra and Alcedo have active fault systems. The Sierra Negra fault is associated with a sill 2 km (1.2 mi) below the caldera. The caldera on Fernandina experienced the largest basaltic volcano collapse in history, with the 1968 phreatomagmatic eruption. Fernandina has also been the most active volcano since 1790, with recent eruptions in 1991, 1995, 2005, and 2009, and the entire surface has been covered in numerous flows since 4.3 Ka. The western volcanoes have numerous tuff cones.