 There are at least five prominent accounts of the fundamental principles of the common law of contracts. The first, and most famous, holds that contract law enforces the basic moral duty to keep promises. A related though distinct view presents contract law as enforcing a duty not to harm others. A third conceives of the law not as enforcing parties’ non-legal duties, but as promoting efficient investment and exchange. An association with economic theory gives this approach a prominence in legal scholarship that outstrips the philosophical attention it has received. A fourth position emphasizes that contracts establish a distinctive relationship between the parties to them and grounds contractual obligations in the value of acting jointly and cooperatively with others. A fifth position is pluralistic and proposes that contract law has many fundamental goals that need not be jointly satisfiable or even consistent. These competing views can be evaluated along several dimensions, including “fit” with actual doctrine, success in justifying the law, and internal coherence.