The Bismarck Sea (German: Bismarcksee, pronounced ['bɪsmarkzeː]) lies in the south-western Pacific Ocean within the Papua New Guinean exclusive economic zone.

[4] The International Hydrographic Organization defines the Bismarck Sea as "that area of the South Pacific Ocean off the northeast coast of New Guinea", with the following limits:[5] On the North and East.

[6] Recent explorations in the Bismarck Sea seabed have yielded discoveries of mineral-rich beds of sulfides, copper, zinc, silver and gold.

[7] Some 5,200 km2 of the Bismarck Sea, between the north-eastern end of New Britain and New Ireland, has been recognised as an Important Bird Area (IBA) by BirdLife International because it apparently supports a population of Beck's petrels, following sightings at sea of this rare and enigmatic species, of which the breeding grounds remain undiscovered.

[8] It was the site of a major Japanese naval defeat in the Battle of the Bismarck Sea during World War II on 3 and 4 March 1943.