The island of New Guinea is the mountainous margin of the Australian continent. Paleozoic and Proterozoic Australian craton extends northward beneath the shallow waters of the Arafura Sea to underlie the southern plains of New Guinea and, with overlying sediments, to form the dramatically sculpted southern slopes of the central range in a great fold and thrust belt. The fold and thrust belt marks the outer limit of the autochthon. Beyond, to the N, E and W, is an aggregation of terranes that have accreted since the Late Cretaceous, driven by oblique convergence between the Pacific and Indo-Australian plates. The terranes comprise continental fragments and blocks of oceanic volcanic arc and of oceanic crust and mantle origin, and include two great ophiolites. The plate boundary itself is a complex system of microplates, each with separate motion, and marked by every kind of plate boundary. In the E the opening of the Manus Basin is associated with rapid clockwise rotation of New Britain, and the opening of the Woodlark Basin causes extension of continental crust in the Papuan peninsula and islands. This has resulted in the development of low-angle extensional faults and domal structures in metamorphic rocks and the exhumation of Pliocene eclogite. Remarkably similar extensional structures and the exhumation of Pliocene eclogite are seen in the Bird’s Head area of western New Guinea (Wandamen Peninsula). Flat and shallow oblique subduction at the New Guinea Trench has caused the deformation of Plio- Quaternary sediments in the Mamberamo Basin, deformation and Pliocene igneous activity in the central range, and the southwestward motion of the Bird’s Head. The island has significant resources of economic minerals and hydrocarbons.