International law has developed as a system of legal rules and principles regulating relations between States. At its core is the principle of the sovereign equality of States and their sovereignty over territory within their own boundaries. Whereas international relations are continually exposed to political change, international law aims to work towards facilitating legal stability in order to prevent or reduce conflicts and offer peaceful settlement of international disputes. The Anthropocene introduces unprecedented new challenges for international law: changes at the Earth System level, not only at the political level. Today’s international law is a system of legal rules resting on foundations that evolved under the circumstances of the late Holocene, assumed to be ever-lasting. These changes will soon create a serious gap between international law as it is currently understood, and Earth System conditions that have already moved beyond the Holocene.