Governing Laws. Contracts are mainly governed by state statutory and common (judge-made) law and private law (i.e. the private agreement). Private law principally includes the terms of the agreement between the parties who are exchanging promises. This private law may override many of the rules otherwise established by state law. Statutory law, such as the Statute of Fraud, may require some kinds of contracts be put in writing and executed with particular formalities, for the contract to be enforceable. Otherwise, the parties may enter into a binding agreement without signing a formal written document.