The Earth is undergoing a shift from conditions of the most recent officially accepted geological time interval, the Holocene, to a new planetary state – the Anthropocene. Unlike the overall stability in environmental conditions characterizing the late Holocene, the Anthropocene is seen as characterized by change, uncertainty and instability in the behavior of the Earth system. This may have increasingly high relevance and important consequences for inter-state relations as currently regulated by international law. This chapter discusses some of these consequences, in particular as related to changes in geography, such as due to climate change and sea-level rise, and the resultant implications for international law principles and rules concerning determination of maritime zones, their delimitation and, ultimately, issues of entitlement to land and maritime areas.