Substantive due process is a principle in United States constitutional law that allows courts to establish and protect substantive laws and certain fundamental rights from government interference, even if they are unenumerated elsewhere in the U.S. Constitution. Courts have asserted that such protections stem from the due process clauses of the Fifth and Fourteenth Amendments to the U.S. Constitution, which prohibit the federal and state governments, respectively, from depriving any person of "liberty ... without due process of law." Substantive due process demarcates the line between acts that courts deem subject to government regulation or legislation and those they consider beyond the reach of governmental interference. Whether the Fifth or Fourteenth Amendments were intended to serve that function continues to be a matter of scholarly and judicial discussion and dissent.
Substantive due process is to be distinguished from procedural due process. The distinction arises from the words "of law" in the phrase "due process of law". Procedural due process protects individuals from the coercive power of government by ensuring that adjudication processes, under valid laws, are fair and impartial. Such protections, for example, include sufficient and timely notice of why a party is required to appear before a court or other governmental body, the right to an impartial trier of fact and trier of law, and the right to give testimony and present relevant evidence at hearings. In contrast, substantive due process protects individuals against majoritarian policy enactments that exceed the limits of governmental authority: courts may find that a majority's enactment is not law and cannot be enforced as such, even if the processes of enactment and enforcement were actually fair.
