In recent years, several ‘global spaces’ have (re-)emerged as key theatres of political and legal contestation: the Polar regions, the High Seas (including maritime security and deep seabed mining), the atmosphere (in particular climate change), cyberspace and outer space. In many respects, most of these spaces are among the ‘last frontiers’ of global politics and international law-making. They find themselves thus at the heart of current debates about global governance. As 'global commons’, most of these global spaces are beyond sovereign jurisdiction and warrant special protection. Controlling them promises security-related and/or socio-economic advantages. Simultaneously, their unsustainable use enhances the risk of transnational conflict and environmental damage. The fact that the North Atlantic Treaty Organization has established space (in 2019) and cyber (in 2016) as ‘operational domains’ in addition to land, sea and air underscores their growing strategic importance as potential loci of geopolitical rivalry.