United States v. Carolene Products Company, 304 U.S. 144 (1938), was a case of the United States Supreme Court that upheld the federal government's power to prohibit filled milk from being shipped in interstate commerce. In his majority opinion for the Court, Associate Justice Harlan F. Stone wrote that economic regulations were "presumptively constitutional" under a deferential standard of review known as the "rational basis test".

The case is most notable for Footnote Four, in which Stone wrote that the Court would exercise a stricter standard of review when a law appears on its face to violate a provision of the United States Constitution, restricts the political process in a way that could impede the repeal of an undesirable law, or discriminates against "discrete and insular" minorities. Footnote Four would influence later Supreme Court decisions, and the higher standard of review is now known as "strict scrutiny".

The case dealt with a federal law that prohibited filled milk (skimmed milk compounded with any fat or oil other than milk fat to resemble milk or cream) from being shipped in interstate commerce. The defendant, a company that traded in a form of filled milk consisting of condensed skim milk and coconut oil (which the company labeled "Milnot" or "Milnut"), argued that the law was unconstitutional because of both the Commerce Clause and the Due Process Clause.

In its previous term, the Court had dramatically increased the number of activities considered to be in or to affect interstate commerce. It had also altered its settled jurisprudence in the area of substantive due process, the doctrine dealing with rights not specifically enumerated in the Constitution. The changes meant that many New Deal programs that the Court would previously have struck down as unconstitutional would now be found constitutional.

The defendant company, charged with breaking the law, at trial filed a motion to dismiss on the grounds that the law was unconstitutional. The United States District Court for the Southern District of Illinois granted the defendant's motion, and the Seventh Circuit Court of Appeals affirmed the District Court's ruling.

Justice Harlan Stone, writing for the Court, held that the law was "presumptively constitutional" properly within legislative discretion. It was not for the courts to overrule because it was supported by substantial public-health evidence and was not arbitrary or irrational. In other words, the Court applied a "rational basis" test.

Carolene Products is best known for its Footnote Four, which is considered to be "the most famous footnote in constitutional law." Although the Court had applied minimal scrutiny (rational basis review) to the economic regulation in this case, Footnote Four reserved for other types of cases other, stricter standards of review.

Stone said that legislation aimed at "discrete and insular minorities" without the normal protections of the political process would be one exception to the presumption of constitutionality and justify a heightened standard of judicial review. The idea has greatly influenced jurisprudence on the Equal Protection Clause jurisprudence and judicial review. It recapitulated common law jurisprudence by which evidence of fraud or other significant legal defects in the transaction, such as self-dealing or other impropriety, may justify overturning a rule.