Abstract
This chapter examines the problem of unity and considers how it is possible for one thing to exist in and through a plurality of parts or phases. It begins with a general discussion of the existence of composite things. The chapter considers the view that composite entities are always an 'ontological free lunch', things that can be freely posited without incurring any cost in relation to ontological economy or Ockham's Razor. It looks at the issue of causal redundancy, a consideration which suggests that positing composite entities as fundamental things is in fact quite costly, something to be undertaken only with strong reasons. The chapter examines three candidates for fundamental composite entities: heaps, artifacts, and organisms. It considers question of which sorts of composite things exist at all, whether fundamentally or derivatively. This involves a search for an intelligible principle of composition.