Since 1945 accelerating scientiﬁc, economic, military and environmental changes have exposed the dangers inherent in continuing to rely upon the res nullius principle; benign neglect outside the rule of law has proven to be an inadequate standard by which to govern the commons. Military and economic competition has created pressures to expropriate or claim sovereignty over parts of the commons. Additionally, new frontiers of exploration on the ocean ﬂoor and in space and the growing awareness of environmental harm to the global commons have propelled the question of ownership and management further up the agenda. Newly identiﬁed global commons such as the stratospheric ozone layer and the global climate system are of particular concern because
no single state can own them, but all states are responsible for their over-exploitation and all states are vulnerable to their existence. This so-called tragedy of the commons poses the question: How can 192 territorial, sovereign states rise to the challenge of governing those parts of the planet beyond sovereign control? This is the dilemma, challenge and opportunity discussed in this chapter.