My aspiration in this book is to probe, unpack, and supplement the mental models we use to understand the obligations that arise from promising and contracting. The thesis I advance is straightforward, even if not intuitive. It is this: when people make or exchange promises, they do more than simply bind themselves to a future course of action. They also bind themselves to a method of reasoning about their future course of action, a method that we might call values-balancing reasoning. I have a second, related claim – when a judge evaluates the legal obligations that arise from promising and contracting, implementing legal doctrine in the context of a dispute, the judge also employs a method of reasoning about the determinants of legal obligations. The judge considers the contextual factors and circumstances that determine how doctrine ought to be applied, which also entails a method of valuesbalancing reasoning.