German New Guinea consisted of the northeastern part of the island of New Guinea and several nearby island groups and was the first part of the German colonial empire. The mainland part of the territory, called Kaiser-Wilhelmsland, became a German protectorate in 1884. Other island groups were added subsequently. The Bismarck Archipelago, and the North Solomon Islands were declared a German protectorate in 1885. The Caroline Islands, Palau, and the Mariana Islands were bought from Spain in 1899. German New Guinea annexed the formerly separate German Protectorate of Marshall Islands, which also included Nauru, in 1906. German Samoa, though part of the German colonial empire, was not part of German New Guinea.

New Guinea is the world's second-largest island, with an area of 785,753 km2 (303,381 sq mi). Located in Melanesia in the southwestern Pacific Ocean, the island is separated from Australia by the 150-kilometre wide Torres Strait, though both landmasses lie on the same continental shelf, and were united during episodes of low sea level in the Pleistocene glaciations as the combined landmass of Sahul. Numerous smaller islands are located to the west and east. The island's name was given by Spanish explorer Yñigo Ortiz de Retez during his maritime expedition of 1545 due to the resemblance of the indigenous peoples of the island to those in the African region of Guinea.