The Fifth Amendment’s Due Process Clause has two prongs, one procedural and one substantive. Procedural due process encompasses the process by which legal proceedings are conducted. It requires that all persons who are materially affected by a legal proceeding receive notice of its time, place, and subject matter so that they have an adequate opportunity to prepare. It also requires that legal proceedings be conducted in a fair manner by an impartial judge who will allow the interested parties to fully present their complaints, grievances, and defenses. The procedural prong of the Due Process Clause governs civil, criminal, and administrative proceedings from the pretrial stage through final appeal, and proceedings that produce arbitrary or capricious results will be overturned as unconstitutional.
Substantive due process encompasses the content or substance of particular laws applied during legal proceedings. Before World War II, the U.S. Supreme Court relied on substantive due process to overturn legislation that infringed on a variety of property interests, including the right of employers to determine the wages their employees would be paid and the number of hours they could work. Since World War II, the Supreme Court has relied on substantive due process to protect privacy and autonomy interests of adults, including the right to use contraception and the right to have an abortion.
However, the line separating procedure from substance is not always clear. For example, procedural due process guarantees criminal defendants the right to a fair trial, while substantive due process specifies that twelve jurors must return a unanimous guilty verdict before the death penalty can be imposed. The line is further blurred by judges and lawyers who simply refer to both prongs as “due process,” without any express indication as to whether they mean substantive or procedural.