Substantive Due Process

Substantive due process (SDP) is one of the theories of law through which courts enforce limits on legislative and executive powers and authority. Under American jurisprudence, the avenues for use of this theory by courts are the Due Process Clauses of the Fifth and Fourteenth Amendments, which prohibit the federal and state governments, respectively, from depriving any person of "life, liberty, or property, without due process of law." That is, substantive due process demarcates the line between, on the one hand, acts by persons of a public or private nature that courts hold are subject to public regulations or legislation, and on the other hand, acts that courts place beyond the reach of governmental interference. Whether the Fifth and/or Fourteenth Amendments were intended to serve this function continues to be a matter of scholarly as well as judicial discussion and dissent.

SDP is to be distinguished from procedural due process (PDP). The distinction arises from the phrase "due process of law". PDP aims to protect individuals from the coercive power of government by ensuring that adjudication processes under valid laws are fair and impartial (e.g., the right to sufficient notice, the right to an impartial arbiter, the right to give testimony and admit relevant evidence at hearings, etc.). In contrast, SDP aims to protect individuals against majoritarian policy enactments which exceed the limits of governmental authority—that is, courts find the majority's enactment is not law, and cannot be enforced as such, regardless of how fair the process of enforcement actually is.

The term "substantive due process" was first used explicitly in 1930s legal casebooks as a categorical distinction of selected due process cases, and by 1950 had been mentioned twice in Supreme Court opinions. The term "substantive due process" itself is commonly used in two ways: first, to identify a particular line of case law; and second, to signify a particular political attitude toward judicial review under the two Due Process Clauses.

Much SDP litigation involves legal challenges regarding unenumerated rights which seek particular outcomes instead of merely contesting procedures and their effects; in successful cases, the Supreme Court recognizes a constitutionally-based "liberty" which then renders laws seeking to limit said "liberty" either unenforceable or limited in scope. Critics of SDP decisions usually assert that those liberties ought to be left to the more politically accountable branches of government.