How come, then, the meaning of individuality is one of the oldest and most vexing problems in biology? For millennia, naturalists and philosophers have struggled to define the most fundamental units of living systems and to delimit the precise boundaries of the organisms that inhabit our planet. This difficulty is partly a product of the search for a singular theory that can be used to carve up all of the living world at its joints. But my view is that no such unified theory exists; there’s no single answer to the question: ‘What parts of the world are a part of you as a biological individual, and what parts are not?’ Different accounts of individuality pick out different boundaries, like an overlapping Venn diagram drawn on top of a network of biotic interactions. This isn’t because of uncertainty or a lack of information; rather, the living world just exists in such a way that we need more than one account of individuality to understand it.