A standard of decision is the law's designation of how certain a decisionmaker must be to render a decision. Because all decisionmaking takes place in a world of uncertainty, the law requires every legal actor before making any sort of decision to measure his or her degree of certainty against the applicable standard. Because the law must set standards in every corner of law, where they determine the realization of policy, they prove essential to understanding any branch of law. Because these standards have an intensely practical impact on legal outcomes, they merit careful study by all lawyers.Despite the subject being thus both wide-ranging and critically important, this book is the first to treat it in depth. The book first catalogs the variety of standards that exist in law. A pattern emerges, which advances in cognitive psychology nicely explain.The book then zeros in on the most conspicuous yet peculiarly distinctive of the standards of decision, which is called the standard of proof and which specifies the sureness required of a factfinder to decide that a contested fact exists. After surveying relevant empirical research and past theoretical explanations, the book constructs a new understanding by drawing on recent breakthroughs in the field of logic. Historical and comparative perspectives on the standard of proof then provide angles from which to illuminate the new understanding.In sum, this book synthesizes decades of thinking and research on standards of decision and pushes forward to elaborate and explain the subject. It does so in a way that will be useful to a broad readership among all those who study the law.