In order to perfectly describe the world, it is not enough to speak truly. In this ambitious and ground-breaking book, Theodore Sider argues that for a representation to be fully successful, truth is not enough; the representation must also use the right concepts--concepts that 'carve at the joints'--so that its conceptual structure matches reality's structure. There is an objectively correct way to 'write the book of the world'. According to Sider, metaphysics is primarily about fundamentality rather than necessity, conceptual analysis, or ontology. Fundamentality is understood in terms of structure: the fundamental truths are those truths that involve structural (joint-carving) concepts. Sider argues that part of the theory of structure is an account of how structure connects to other concepts. For example, structure can be used to illuminate laws of nature, explanation, reference, induction, physical geometry, substantivity, conventionality, objectivity, and metametaphysics. Another part is an account of how structure behaves. Since structure is a way of thinking about fundamentality, Sider's account implies distinctive answers to questions about the nature of fundamentality. These answers distinguish his theory of structure from other recent theories of fundamentality, including Kit Fine's theory of ground and reality, the theory of truthmaking, and Jonathan Schaffer's theory of ontological dependence.