Global commons are areas and resources defined as being beyond sovereign jurisdiction. They are socially constructed and this article identifies four: the high seas and deep seabed, Antarctica, outer space and the global atmosphere although attempts to designate new areas as commons are also noted. The construction of global commons, it is argued, has been determined by shifts in human knowledge, capability and perceptions of scarcity. The commons problem, as defined by Hardin and other analysts arises from the ecological consequences of open access, but also from the renewed concerns of strategists about the military use of common spaces. In the international system a primary response has been to extend sovereignty and the degree to which the global commons have been enclosed is assessed. An alternative model is provided by the negotiation of common heritage status, but since the experiment with the deep sea bed this has not found favour in the Arctic, Antarctic and elsewhere. In terms of the continuing management of the commons the international community has resorted to an array of regulatory regimes of varying coverage and effectiveness