Cosmoledo is an atoll of the Aldabra Group and belongs to the Outer Islands of the Seychelles. The atoll is 14.5 km long east-west, and 11.5 km north-south. The total land area is about 5.2 km², while the lagoon measures 145 km² in area (total 152 km²). It is located at 9°42’S 47°36’E. The closest island is Astove Island, 38 km farther south. Cosmoledo Atoll and Astove Island are together sometimes known as Cosmoledo Group, which is part of the larger Aldabra Group.
There are 16 individual islets and cays along the rim of the atoll, with Menai (in the west) and Wizard Island (Grande Île, in the southeast) being the largest.
Cosmoledo holds Seychelles’ largest colonies of all three species of booby that breed in Seychelles. The atoll holds the last viable population of Brown Booby, breeding mainly on Ile du Sud Ouest, with a few on Ile du Nord. It also has the Indian Ocean’s larget population of Red-footed Booby censused by the Island Conservation Society as about 15,000 pairs.