The part of the law that creates, defines, and regulates rights, including, for example, the law of contracts,torts, wills, and real property; the essential substance of rights under law.
Substantive law and procedural law are the two main categories within the law. Substantive law refers to the body of rules that determine the rights and obligations of individuals and collective bodies. Procedural law is the body of legal rules that govern the process for determining the rights of parties.
Substantive law refers to all categories of public and private law, including the law of contracts, real property, torts, and criminal law. For example, criminal law defines certain behavior as illegal and lists the elements the government must prove to convict a person of a crime. In contrast, the rights of an accused person that are guaranteed by the Fourth, Fifth, and Sixth Amendments to the U.S. Constitution are part of a body of criminal procedural law.
U.S. substantive law comes from the common law and from legislative statutes. Until the twentieth century, most substantive law was derived from principles found in judicial decisions. The common-law tradition built upon prior decisions and applied legal precedents to cases with similar fact situations. This tradition was essentially conservative, as the substance of law in a particular area changed little over time.
Substantive law has increased in volume and changed rapidly in the twentieth century as Congress and state legislatures have enacted statutes that displace many common-law principles. In addition, the National Conference of Commissioners on Uniform State Laws and the American Law Institute have proposed numerous model codes and laws for states to adopt. For example, these two groups drafted the uniform commercial code (UCC), which governs commercial transactions. The UCC has been adopted in whole or substantially by all states, replacing the common law and divergent state laws as the authoritative source of substantive commercial law.