Definition
Substantive due process is the doctrine that the Due Process Clauses of the Fifth and Fourteenth Amendments protect certain liberties so fundamental that the government may not infringe them no matter how fair the procedures it uses. Where procedural due process asks how the government may act, substantive due process asks whether the government may pursue a particular end at all.
The doctrine treats the word liberty in the Due Process Clause as protecting more than freedom from physical restraint. Courts have located within it a set of fundamental rights, including rights relating to marriage, family, child-rearing, and bodily autonomy, that receive heightened constitutional protection.
Why it matters
How it works
When a law burdens a right the courts have recognized as fundamental, it is reviewed under strict scrutiny and will be upheld only if it is narrowly tailored to serve a compelling government interest. Laws affecting non-fundamental interests receive only rational basis review, a far more deferential standard. The central and difficult question is how courts identify which rights count as fundamental; one influential approach asks whether a right is deeply rooted in the nation's history and tradition.