This book provides a comprehensive investigation into the concept of typicality and its significance for physics and the philosophy of science. It identifies typicality as a fundamental way of reasoning, central to how natural laws explain and are tested against phenomena. The book discusses various applications of typicality to foundational questions in physics and beyond.These include:a unified interpretation of objective probabilities in classical mechanics and quantum mechanicsa detailed discussion of Boltzmann's statistical mechanics, entropy, and the second law of thermodynamicsa novel account of the asymmetry of causation and the arrow of time Finally, the book turns to the question: "What are laws of nature"? It argues that typicality extends to a powerful way of reasoning in metaphysics that can and should inform our commitments about the fundamental ontology of the world. On this basis, it develops an argument against theHumean best system account, according to which laws of nature are merely an efficient summary of contingent regularities.