When Oklahoma banned beer sales to men under 21 but let women buy at 18, the Supreme Court used it as the vehicle to create a new legal test. In Craig v. Boren (1976), the Court ruled that laws classifying people by sex must serve an "important governmental objective" and be "substantially related" to achieving it -- a standard now called intermediate scrutiny. It sits between the easy-to-pass rational basis test (used for most economic regulations) and strict scrutiny (used for race-based classifications, which almost never survive). Twenty years later, in United States v. Virginia (1996), Justice Ruth Bader Ginsburg tightened the standard further when the Court ordered the Virginia Military Institute to admit women, requiring the government to show an "exceedingly persuasive justification" for any sex-based classification. Intermediate scrutiny matters because it determines how hard a government must work to defend treating men and women differently. Laws challenged under this standard -- covering everything from military draft registration to single-sex education -- do not get a free pass, but they do not face the near-automatic rejection that racial classifications do.