This article examines three concepts that have emerged to respond to collective environmental concerns:‘common areas’, ‘common heritage’, and ‘common concern’. As will become apparent, the impact of these three concepts has been felt less in the development and application of customary law than in the development of treaty-based regimes. Today, such regimes institutionalise many collective environmental concerns, and provide settings in which states' commitments can be adjusted and refined on an ongoing basis. Within these regimes, it has also been possible to develop compliance procedures that are actually invoked and which reflect the collective nature of states' interest in environmental protection. To protect areas or resources beyond state jurisdiction, and to address common environmental concerns, international environmental law has not merely had to undergo a significant conceptual expansion, but has also had to do so against the grain of the foundational structures of international law.