The Territory of Ashmore and Cartier Islands are two groups of small low-lying uninhabited tropical islands in the Indian Ocean situated on the edge of the continental shelf north-west of Australia and south of the Indonesian island of Roti at .
The territory includes Ashmore Reef (West, Middle, and East Islets) and Cartier Island (70 km east) with, a total area of 199.45 km² within the reefs and including the lagoons, and 114,400 m² of dry land. While they have a total of 74.1 km of shoreline, measured along the outer edge of the reef, there are no ports or harbors, only offshore anchorage. Nearby Hibernia Reef, 42 km Northeast of Ashmore Reef, is not part of the territory. It has no permanently dry land area, although large parts of the reef become exposed during low tide.
There is an automatic weather station on West Islet.
Ashmore Reef is called Pulau Pasir by Indonesians, and considered part of Rote Ndao Regency of East Nusa Tenggara province. In the Rote Island language, it is called Nusa Solokaek. Both names have the meaning Sand Island.
The Ashmore Reef Marine National Nature Reserve was established in August 1983. It is of significant biodiversity value as it is in the flow of the Indonesian throughflow current from the Pacific Ocean through the Indonesian Archipelago to the Indian Ocean. It is also in a surface current west from the Arafura Sea and Timor Sea. There are 14 distinct species of sea snake in the area, more than in any other area. There is also an unusually high level of species diversity of coral, mollusks, and fish. A memorandum of understanding between the Australian and Indonesian governments allows Indonesian fishermen access to their traditional fishing grounds within the region, subject to limits.
Cartier Island Marine Reserve includes the entire sand cay of Cartier Island, the reef surrounding it, the ocean for a 7.2 km radius around the island, and 1000 m below the seafloor. It was proclaimed in 2000.
A number of things were done to discourage the practice such as attempting to have the people smugglers arrested in Indonesia; the so-called Pacific Solution of processing them in third countries; the boarding and forced turnaround of the boats by Australian military forces, and finally excising Ashmore and many other small islands from the Australian migration zone. Two boatloads of asylum seekers were each detained for several days in the lagoon at Ashmore after failed attempts by the Royal Australian Navy to turn them back to Indonesia in October 2001.