Where are the edges of a tree? What makes arms different from daughters? What have corals got in common with Necker cubes? Biological individuality has become a dizzying topic since researchers began, at the turn of the millennium, to realize that we can't go on taking organisms for granted as basic particles of the living world. Ellen Clarke takes us on a disorienting romp through the natural world and argues that our way of conceptualizing living things-of understanding life as carved up into separate chunks-is best understood as an idealization. Vivid examples animate some fairly arcane philosophical topics concerning identity over time, natural kinds, and the fundamental furniture of reality, as well as serious biological issues concerning natural selection, the emergence of compositional hierarchies, and the evolution of cooperation. Readers will come away with newfound respect for humankind's ingenuity in engineering concepts that make sense of the complex and ever-changing wonders of life on earth.