Rules are a central component of such diverse enterprises as law, morality, language, games, religion, etiquette, and family governance, but there is often confusion about what a rule is, and what rules do. Offering a comprehensive philosophical analysis of these questions, this book challenges much of the existing legal, jurisprudential, and philosophical literature, by seeing a significant role for rules, an equally significant role for their stricter operation, and making the case for rules as devices for the allocation of power among decision-makers.