In U.S. constitutional law, when a law infringes upon a fundamental constitutional right, the court may apply the strict scrutiny standard. Strict scrutiny holds the challenged law as presumptively invalid unless the government can demonstrate that the law or regulation is necessary to achieve a "compelling state interest". The government must also demonstrate that the law is "narrowly tailored" to achieve that compelling purpose, and that it uses the "least restrictive means" to achieve that purpose. Failure to meet this standard will result in striking the law as unconstitutional.

Strict scrutiny is the highest and most stringent standard of judicial review in the United States and is part of the levels of judicial scrutiny that US courts use to determine whether a constitutional right or principle should give way to the government's interest against observance of the principle. The lesser standards are rational basis review and exacting or intermediate scrutiny. These standards are applied to statutes and government action at all levels of government within the United States.

The notion of "levels of judicial scrutiny", including strict scrutiny, was introduced in Footnote 4 of the U.S. Supreme Court decision in United States v. Carolene Products Co. (1938), one of a series of decisions testing the constitutionality of New Deal legislation. One of the most notable cases in which the Supreme Court applied the strict scrutiny standard and found the government's actions constitutional was Korematsu v. United States (1944), since overruled, in which the Court upheld the forced relocation of Japanese Americans in internment camps during World War II. Another example is the D.C. Circuit Court's 2007 ruling in Abigail Alliance v. von Eschenbach that compelling government interest was demonstrated in the restriction of unapproved prescription drugs.

The burden of proof falls on the state in cases that require strict scrutiny or intermediate scrutiny, but not the rational basis.

U.S. courts apply the strict scrutiny standard in two contexts:

To satisfy the strict scrutiny standard, the law or policy must:

Legal scholars, including judges and professors, often say that strict scrutiny is "strict in theory, fatal in fact", since popular perception is that most laws subjected to the standard are struck down. Sandra Day O'Connor explicitly denied this in Adarand Constructors, Inc. v. Peña in 1995, and an empirical study of strict scrutiny decisions in the federal courts found that laws survive strict scrutiny more than 30% of the time. In one area of law, religious liberty, laws that burden religious liberty survived strict scrutiny review in nearly 60% of cases; however, a discrepancy was found in the type of religious liberty claim, with most claims for exemption from law failing and no allegedly discriminatory laws surviving.

Harvard law professor Richard Fallon Jr. has written that rather than being neatly applied, under strict scrutiny, "interpretation is more varied than is often recognized", a view that has been acknowledged by U.S. Supreme Court Justice Clarence Thomas (e.g., in his dissent (part III) in Hellerstedt). The compelling state interest test is distinguishable from the rational basis test, which involves claims that do not involve a suspect class or fundamental right, but still arise under the Equal Protection Clause or Due Process Clause. A presumption of constitutionality does not apply under strict scrutiny: the burden to prove the constitutionality of a law shifts to the government lawyers.