The Coral Sea Islands Territory includes a group of small uninhabited tropical islands and reefs in the Coral Sea, northeast of Queensland, Australia. The territory covers 780,000 sq km, extending east and south from the outer edge of the Great Barrier Reef, and include Heralds Beacon Island, Osprey Reef, the Willis Group, and fifteen other reef/island groups.

The Coral Sea Islands were first charted in 1803; in the 1870 and 1880s the islands were mined for guano but the absence of a permanent supply of fresh water prevented long-term habitation. The territory was created in 1969 by the Coral Sea Islands Act (before, the area was considered part of Queensland) and extended in 1997 to include Elizabeth and Middleton Reefs nearly 800 km further South, already in the Tasman Sea. The two latter reefs are much closer to Lord Howe Island, New South Wales (about 150 km) than to the southernmost island of the rest of the territory, Cato Island. The islands, cays and reefs of the Great Barrier Reef are not part of the territory, belonging to Queensland instead. The outer edge of the Great Barrier Reef is the boundary between Queensland and the Coral Sea Islands Territory.

The territory is a possession of Australia, administered from Canberra by the Territories section of the Department of Transport and Regional Services. Defence is the responsibility of Australia, and the territory is visited regularly by the Royal Australian Navy. Australia maintains automatic weather stations on many of the isles and reefs, and claims a 200 nautical mile (370 km) exclusive fishing zone. There is no economic activity, and only a staff of three or four people to run the meteorological station on Willis Island (South Islet), established in 1921.

There are about 30 separate reefs and atolls, twelve being wholly submerged or drying only during low tide, and 18 others with a total of about 51 islets and cays (18 alone on the atoll Lihou Reef and Cays), some of which are vegetated.The coral Sea is 3.9 miles deep The atolls exhibit a wide range of size, from a few kilometres in diameter to perhaps the second largest atoll in the world by total area (including lagoon): Lihou Reef, with a lagoon size of 100 by 30 km and an area of 2,500 km², which compares to a combined land area of the 18 individual islets of only 0.91 km². The islands are all very low. The territory's FIPS 10-4 code is CR, whereas ISO 3166 includes it in Australia (AU).

The Willis Islets are important nesting areas for birds and turtles, but their natural resources are negligible. They comprise less than three square kilometres of land. There is no port or harbour, only offshore anchorage.

Most of the atolls fall into two groups, while Mellish Reef to the east, and Middleton Reef and Elizabeth Reef to the south are grouped separately:

Northwestern Group

1. Osprey Reef (submerged atoll roughly oval in shape, measuring 25 by 12 km, covering around 195 km², with lagoon up to 30 m deep)

2. Shark Reef (small elongated submerged reef 15 km South of Osprey Reef, with a least depth of 7.8 m)

3. Bougainville Reef (small submerged atoll, 2.5 by 4 km, area 8 km² with lagoon, dries at half tide)

4. East Holmes Reef (submerged atoll, about 14 by 10 km, area 125 km² with lagoon)

5. West Holmes Reef (submerged atoll 6 km East of East Holmes Reef, about 18 by 7 km, area 125 km² with lagoon that is open on the West side, two small cays)

6. Flora Reef (small submerged atoll, 5 by 4 km, about 12 km²)

7. Diane Bank (sunken atoll, depths of less than 10 m over an area of 65 by 25 km, or 1300 km², along the northern edge 3 m deep, with Sand Cay in the Northwest, 3 m high)

8. North Moore Reef (small submerged atoll, 4 by 3 km, area 8 km² including lagoon that is open on the Northwest side)

9. South Moore Reef (small submerged reef 5 km South of North Moore Reef)

10. Willis Islets (sunken atoll, bank 45 by 19 km, bank area more than 500 km², 3 islets on the Northwestern side: North Cay, Mid Islet almost 8 m high, South Islet or Willis Island 10 m high)

11. Magdelaine Cays & Coringa Islets (one large, partially sunken atoll structure, almost 90 by 30 km, bank area about 1500 km², 2 islets of the Magdelaine Cays in the North: North West Islet (area approximately 0.2 km²) and South East Cay (area 0.37 km²); 2 islets of the Coringa Islets 50 to 60 km further Southwest: Southwest Islet or Coringa Islet (area 0.173 km²), and Chilcott Islet (area 0.163 km²))

12. Herald Cays, Northeast Cay (encircled by a reef of 3 by 3 km, total area 6 km², land area 0.34 km²)

13. Herald Cays, Southwest Cay (4 km Southwest of Northeast Cay, encircled by a reef of 2 by 2 km, total area 3 km², land area 0.188 km²)

14. Lihou Reef and Cays (largest atoll in the coral sea, with a size of 2500 km², land area 0.91 km²)

15. Diamond Islets & Tregosse Reefs (large, partially sunken atoll, 100 by 52 km, area of the bank over 3000 km², with 4 islets and 2 small submerged reefs in the Northeast and Southeast: West Diamond Islet, Central Diamond Islet, East Diamond Islet on the Northeastern rim of the former atoll, and South Diamond Islet, East Tregosse Reef and West Tregosse Reef on the Southern rim)

16. North Flinders Reef (large atoll, 34 by 23 km, area 600 km², with 2 islets, Flinders Cay being the larger one with a length of 200 m and a height of 3 m)

17. South Flinders Reef (atoll, 15 by 5 km, 60 km²)

18. Herald's Surprise (small submerged reef North of Flinders Reefs, 3 by 2 km)

19. Dart Reef (small submerged reef Northwest of Flinders Reefs, 3 by 3 km, area 6 km² including small lagoon that is open to the North)

20. Malay Reef (small submerged reef, not clearly defined, no breakers, difficult to see)

21. Abington Reef (submerged reef, nearly awash, 4 by 2.5 km, area 7 km²)

22. Marion Reef (large circular atoll formation that is comprised of three main units located on the Eastern side: Marion, Long and Wansfell; and a number of smaller reefs on the west. The formation sits atop a submarine feature known as the Marion Plateau which is separated from the larger Coral Sea Plateau to the north by the Townsville Trough. Three small sand cays are located on the eastern side of Marion Reef: Paget Cay, on Long Reef, Carola Cay, south of Long Reef, and Brodie Cay, on Wansfell Reef.

The atolls of the Northwestern Group, except Osprey Reef and Shark Reef in the North, and Marion Reef in the South, are located on the Coral Sea Plateau (Queensland Plateau), a contiguous area of depths less than 1000 m.

Flinders Reefs (North and South), Herald's Surprise and Dart Reef form a cluster of reefs of 66 by 26 km.

Magdelaine Cays, Coringa Islets and Herald Cays are part of the 8856 km² Coringa-Herald National Nature Reserve, created on August 16, 1982 and located around 400 km east of Cairns and 220 to 320 km from the outer edge of the Great Barrier Reef. The 6 islets of the nature reserve have areas from 0.16 to 0.37 km², for a total of 1.24 km².

Lihou Reef was declared a Nature Reserve on August 16, 1982, with an area of 8440 km².

The Nature Reserves were created to protect wildlife in the respective areas of the territory.

Mellish Reef

1. Mellish Reef, being about 300 kilometres to the east of the Northwestern Group, thus the most distant from the Australian continent of all the reefs and atolls of the Coral Sea Islands Territory, is not considered to be part of any group. It has the outline of a boomerang-shaped platform around 10 km in length and 3 km across, area 25 km². The surrounding reefs, which enclose a narrow lagoon, are completely submerged at high tide. Near the centre of the lagoon is the only permanent land of the reef - Heralds-Beacon Islet. The island is a small cay measuring 600 m by 120 m, area 57,000 m², only rising a few meters above the high water mark.

Southeasterly Group

1. Frederick Reefs: The reefs form a semi-enclosed lagoon, known as Anchorage Sound, with an opening on the North side. The complex measures about 10 by 4 km, with an area of 30 km². On the southern side of the reef lies Observatory Cay, the only permanently dry land, although there are a few of others cays that can be awash at high tide.

2. Kenn Reef, submerged atoll of about 15 by 8 km, area 40 km², islet Observatory Cay in the Southeast, 2 m high

3. Saumarez Reefs, southernmost reefs to be located on the Coral Sea Shelf; three main reefs and numerous smaller reefs that form a large crescent-shaped formation open to the northwest, about 27 by 14 km, area less than 300 km². There are two sand cays: North East Cay and South West Cay.

4. Wreck Reefs: atoll 25 by 5 km, area 75 km², open on the North. Islets found on the reefs include Bird Islet, West Islet and Porpoise Cay.

5. Cato Reef: Cato bank 21 by 13 km, area 200 km² of depths less than 17 m; Cato Reef encircles an area of 3.3 by 1.8 km, area 5 km² including lagoon; Cato Island, in the West of the lagoon, 650 by 300 m, area 1.5 km², 6 m high. Close to the Southeast corner of Cato bank is Hutchison Rock, with 1 m depth over it.

Extreme South

Elizabeth and Middleton Reefs, together with reefs around Lord Howe Island (New South Wales) 150 km to the south, are regarded as the southernmost coral reefs in the world. Their location, where tropical and temperate ocean currents meet, contributes to an unusually diverse assemblage of marine species. These mostly submerged atolls which dry only during low tide were added to the territory only in 1989. They are located on the Lord Howe Rise in the Tasman Sea which joins the Coral Sea in the South. Already on December 23, 1987, they were protected as Elizabeth and Middleton Reefs Marine National Nature Reserve, which has an area of 1880 km².
 

1. Middleton Reef, atoll about 8.9 by 6.3 km, area 37 km² including lagoon, one islet: Elizabeth island (Elizabeth cay), no vegetation, 600 meters by 400 meters (area 0.2 km²), highest point close to the Northern end 1.5 meters. At low tides much of the reef flat is exposed.

2. Elizabeth Reef, atoll about 8.2 by 5.5 km, area 51 km² including lagoon, one islet: The Sound, 100 by 70 meters (area 5,000 m²), highest point 0.8 meters. At low tides much of the reef flat is exposed.

Overview of Islets and Cays

Automatic, unmanned weather stations are located on following reefs or atolls:

Lighthouses are located on following reefs or islands: