Book excerpt: Lynne Rudder Baker presents and defends a unique account of the material world: the Constitution View. In contrast to leading metaphysical views that take everyday things to be either non-existent or reducible to micro-objects, the Constitution View construes familiar things as irreducible parts of reality. Although they are ultimately constituted by microphysical particles, everyday objects are neither identical to, nor reducible to, the aggregates of microphysical particles that constitute them. The result is genuine ontological diversity: people, bacteria, donkeys, mountains and microscopes are fundamentally different kinds of things - all constituted by, but not identical to, aggregates of particles. Baker supports her account with discussions of non-reductive causation, vagueness, mereology, artefacts, three-dimensionalism, ontological novelty, ontological levels and emergence. The upshot is a unified ontological theory of the entire material world that irreducibly contains people, as well as non-human living things and inanimate objects.