Many leading environmental and security concerns now facing the international community may be traced to the frontiers, that is, the areas historically outside of national jurisdiction including the deep seabed, outer space, Antarctica, the atmosphere, and some argue, cyberspace. From climate change and cyber attacks to the associated challenges of space weaponization and orbital debris mitigation, solutions to all of these issues have at their root some form of regulation over the frontiers, sometimes – though not always accurately – called the “global commons.” Governance is transitioning away from consensual United Nations–centered multilateral treaties to regional and bilateral accords. These burgeoning regime complexes are being influenced by the multipolar state of international relations, advancing technology, and resource scarcity. Environmental and security challenges are proliferating as a result of governance being in flux. This chapter distills recent research on these topics and makes an original contribution by comparing and contrasting some of the principal issues facing these frontiers of the international community, analyzing how and why existing governance structures are often failing to adequately meet global collective action problems, and proposing a new way forward incorporating lessons from successful regimes as well as the interdisciplinary scholarship on polycentric governance.