The Anthropocene is something of a ‘game-changer’ for the way we can and should view international relations. It suggests the need to step back and reconsider some of the core assumptions we have about the way the world works. In the context of the Anthropocene, this means that the environment is no longer a background to geopolitics, but rather a dynamic force that impacts global politics. This chapter makes the case that the Anthropocene compels us to view and approach security not through the lens of how we might protect human collectives or institutions, but how we might protect ecosystems themselves. Consequentially, this points to a defence of ecosystems, in particular their functionality in the face of ongoing change. For doing so, the chapter outlines the contours of an ecological security discourse, emphasising its focus on the resilience of ecosystems and the rights and needs of the most vulnerable.