Contract law has traditionally been governed by common law (case law), although many important areas have been superseded by statute in recent years.
All states except Louisiana have largely adopted the provisions of the Uniform Commercial Code (UCC), which governs many aspects of various commercial transactions. Article 2, which governs sales, is the section of primary importance to basic contracts courses.
A persuasive but not binding source of contract law is the Second Restatement of Contracts of 1980, which replaced the 1932 Restatement of Contracts. It is an annotated summary of common law by the American Law Institute. However, the law in a given jurisdiction is not necessarily that propounded by the Restatement.