Seychelles is a small island country east of the African continent located in the Sea of Zanj due north of Madagascar, with Antsiranana as its nearest foreign city. Seychelles lies between approximately 4ºS and 10ºS and 46ºE and 54ºE. The nation is an archipelago of 155 tropical islands, some granite and some coral, the majority of which are small and uninhabited. The landmass is only 452 km² (175 mi²) but the islands are spread wide over an exclusive economic zone of 1,336,559 km² (516,048 mi²). About 90 percent of the population of 100,000 live on Mahé, 9 percent on Praslin and La Digue. Around a third of the land area is the island of Mahé and a further third the atoll of Aldabra.

There are two distinct regions, the granitic islands, the world's only oceanic islands of granitic rock and the coralline outer islands. The granite islands are the world's oldest ocean islands, while the outer islands are mainly very young, though the Aldabra group and St Pierre (Farquhar Group) are unusual, raised coral islands that have emerged and submerged several times during their long history, the most recent submergence dating from about 125,000 years ago

The archipelago consists of 155 islands and thirty prominent rock formations scattered throughout a self-proclaimed exclusive economic zone of more than 1,350,000 square kilometres (520,000 sq mi) of ocean. Some forty islands are granitic and lie in a 90-kilometre (56 mi) radius from Mahé, the main island. The remaining islands are coralline, stretching over a 1,200-kilometre (750 mi) radius from Ile Aux Vaches in the northeast to the Aldabra Atoll in the southwest. The country's Inner Islands are the granitic islands plus two nearby coralline islands, Bird Island and Denis Island.^{[citation needed]} The remaining coralline islands are the Outer Islands.^{[citation needed]} The islands are all small—the aggregate land area is only 455 square kilometres (176 sq mi).

Mahé is 25 kilometres (16 mi) long and no more than 8 kilometres (5.0 mi) wide, with an area of 156.7 km² (61 sq mi).^{[citation needed]} It contains the capital and only city, Victoria, an excellent port. Victoria lies approximately 1,600 kilometres (990 mi) east of Mombasa, Kenya; 2,800 kilometres (1,700 mi) southwest of Mumbai; 1,700 kilometres (1,100 mi) north of Mauritius; and 920 kilometres (570 mi) northeast of Madagascar. The only other important islands by virtue of their size and population are Praslin and La Digue, situated about thirty kilometers to the northeast of Mahé.

The granitic islands are founded on a fragment separated from the Indian continental plate during the Palaeocene about 66 million years ago during the break up of the supercontinent of Gondwana. This break-up was associated with the volcanic activity that built the Mascarene Plateau. These granitic islands are characterized by boulder-covered hills and mountains as high as 940 metres (3,080 ft) rising abruptly from the sea. Elsewhere, narrow coastal plains extend to the base of the foothills. Extensively developed coral reefs are found mainly on the east coasts because of the southwest trade winds and equatorial current. Ninety-nine percent of the population is located on the granitic islands, and most are on Mahé.

The coralline islands differ sharply from the granitic in that they are very flat, often rising only a few feet (one meter) above sea level. They have no fresh water, and very few have a resident population. Many, like Ile aux Vaches, Ile Denis, the Amirante Isles, Platte Island, and Coetivy Island, are sand cays upon which extensive coconut plantations have been established. Some of the coralline islands consist of uplifted reefs and atolls covered with stunted vegetation. Several of these islands have been important breeding grounds for turtles and birds, as well as the sites of extensive guano deposits, which formerly constituted an important element of the Seychellois economy but now for the most part are depleted. The Aldabra Islands, the largest coralline atoll with an area greater than Mahe, are a sanctuary for rare animals and birds.

The five groups of coralline islands that make up the Outer Islands are Southern Coral Group (a collective term for Île Platte and Coëtivy Island), Amirante Islands, Alphonse Group (Alphonse Atoll and St. François Atoll), Aldabra Group (Aldabra Atoll, Assumption Island, and the Cosmoledo Group, consisting of Cosmoledo Atoll and Astove Island), and Farquhar Group (Farquhar Atoll, Providence Atoll and St. Pierre Island).

The Seychelles Bank is founded on a granite basement, a fragment separated from the Indian continental plate during the Palaeocene about 66 million years ago. This break-up was associated with the volcanic activity that built the Mascarene Plateau. The occurrence of syenite, diorite and microgranite in the western part of the Seychelles Bank could indicate that crustal deposit across the northwestern Indian Ocean Ridge apparently drove the Seychelles block southwestwards, causing it to collide with the northeastern edge of the Mascarene Basin. This collision could have led to the development of the Amirante Trough. This rift formation is associated with the Réunion hotspot which is also responsible for Réunion Island and the Deccan Traps in India. Because of its long isolation, the Seychelles hosts several unique species including the coco de mer, a palm which has the largest seeds of any plant and the world's largest population of giant tortoises.^{[citation needed]}