Bismarck Archipelago, a crescent-shaped group of islands in the South Pacific, northeast of New Guinea. They lie just south of the Equator and stretch more than 300 miles (480 km) from north to south and almost 600 miles (960 km) east to west. In all there are about 200 islands, with an area of 18,700 square miles (48,400 km2). Adjacent waters include the Bismarck and Solomon seas.

The largest island in the group is New Britain. With small nearby islands it has an area of about 14,100 square miles (36,500 km2) and a population of 311,955. The second largest is New Ireland, covering 3,800 square miles (9,840 km2); it has a population of 87,194. Other sizable islands are Manus, in the Admiralty Islands; New Hanover; Umboi; and Mussau, in the St. Matthias Group.

The islands are mountainous. The highest peak, rising 8,000 feet (2,438 m) above sea level, is on New Britain. Rivers are short and swift. Jungle plants thrive in the hot humid climate.

Most of the inhabitants are Melanesian. The largest settlement is Rabaul, with a population of 17,022, on New Britain. The raising of coconuts, coffee, and other tropical crops is the main economic activity.

Germany annexed the archipelago in 1884 and named it in honor of Prince Otto von Bismarck. In 1920, after World War I, a League of Nations mandate placed the islands under Australian control. Japan seized them in 1942. The Allies captured New Britain and the Admiralties in 1943–44, but bypassed the other islands. In 1946 the islands were again placed under Australian administration as part of the Trust Territory of New Guinea, created by the United Nations. Since 1949 they have been administratively a part of what is now Papua New Guinea, which was granted independence by Australia in 1975.