Papua New Guinea lies wholly within the southern tropics 160 kilometres north of Australia and comprises the eastern half of the island of New Guinea and some 600 offshore islands. With a total land area of approximately 465,000 square kilometres, Papua New Guinea is the largest country in the South Pacific region, after Australia.

The mainland and larger islands are mountainous and rugged. The highest mountain range rises to more than 4,700 meters. Interspersed in the complex of ranges on the mainland are large upland valleys. The mountains are the sources of fast-flowing rivers that descend to the coastal plains to form some of the largest river systems of the world. The largest, the Sepik and the Fly rivers, are navigable for upward of 800 kilometres. A line of active volcanoes stretches along the north coast of the mainland. The coastline is ringed by coral reefs. Vegetation changes from swamps and savanna grasslands on the coast through tropical rain forest to moss, alphine forest and grasslands in the highlands.

Port Moresby, the national capital, is the major city and the centre of government and commerce. The second city, Lae, is the main industrial centre and is the gateway to the populous highlands region.

The climate is tropical and monsoonal with only two seasons, the wet and the dry. Rainfall varies from 102 centimetres per annum in the Port Moresby area to more than 510 centimetres per annum in some other areas. Although sources differ, temperatures seem to range from 20ºC to 35ºC in the coastal areas and from 4ºC to 30ºC in the highlands.

Natural hazards
Papua New Guinea is situated along the Pacific 'Rim of Fire' and is therefore subject to active volcanism. In addition, the country is subject to frequent and sometimes severe earthquakes, mud slides and tsunamis.