island group in the South Pacific Ocean, about 500 miles (800 km) east of New Zealand. Composed of 10 islands, they are primarily of volcanic formation, but areas of limestone indicate that they may once have been part of New Zealand. Chatham Island, the largest (347 square miles 【900 square km】), rises to 942 feet (287 metres); more than 20 percent of its poorly drained surface is covered by shallow lagoons. Pitt Island (about 24 square miles 【62 square km】) lies 13 miles (21 km) from Chatham. Tarakoikoia is a rock pinnacle to the southeast rising abruptly to 566 feet (172 metres).

There are no indigenous mammals, and the reptiles are of New Zealand species. The original forest vegetation has been seriously modified by fires and grazing since the arrival of Europeans; large areas are now under English grasses, while much of the rest is swamp, heath, and dune. The climate is cool and humid.

William R. Broughton discovered the group in 1791 while en route to Tahiti in the British ship Chatham. Sealing and whaling stations were soon established, the latter surviving until 1861. In 1865 sheep were introduced, and, although the industry has been limited by isolation, the export of wool and breeding stock is now the basis of the islands' economy. Other sources of income are blue cod and crayfish in the local waters. There are an estimated 10,000 acres (4,000 hectares) of moorland peat, which were being studied for possible commercial application.

Annexed by New Zealand in 1842, the group is administered by a resident commissioner appointed by the Department of Maori and Island Affairs. The populace, dominantly European with some Maori (who replaced the indigenous Moriori in 1835), is served by several schools and a hospital in the chief settlement, Waitangi, on Chatham Island. Area 372 square miles (963 square km). Pop. (2001) 717.