State power to define women's sports by biological sex is constitutionally sound under the Tenth Amendment and Title IX as originally understood.

The question in these consolidated cases is whether the Equal Protection Clause or Title IX preempts state laws that define eligibility for women's sports teams by biological sex. The Constitution’s text and original meaning answer: No. Relevant constitutional text: The Fourteenth Amendment, Section 1, provides that ‘No State shall make or enforce any law which shall abridge the privileges or immunities of citizens of the United States; nor shall any State deprive any person of life, liberty, or property, without due process of law; nor deny to any person within its jurisdiction the equal protection of the laws.’ The Tenth Amendment reserves to the States powers not delegated to the United States. Title IX (20 U.S.C. §1681(a)) bars discrimination ‘on the basis of sex’ in federally funded education programs. Ratification-era understanding: The Equal Protection Clause, ratified in 1868, was originally aimed at laws discriminating against newly freed slaves; ‘sex’ was not within its core concern, and early Congresses and courts did not apply heightened scrutiny to sex classifications. The Tenth Amendment was understood to leave family, education, and public health to the States. Title IX, enacted in 1972, used ‘sex’ in its ordinary biological sense; the accompanying regulations (34 CFR §106.41) explicitly allowed sex-separate teams in contact sports and where selection is based on competitive skill. Holding: State laws like West Virginia’s Save Women’s Sports Act and Idaho’s Fairness in Women’s Sports Act, which define women’s and girls’ sports teams by biological sex, do not violate the Equal Protection Clause because they fall within the traditional police powers reserved by the Tenth Amendment and are consistent with the plain meaning of Title IX, which permits sex-separate teams based on biological differences. The Fourth Circuit and Ninth Circuit decisions are reversed; West Virginia and Idaho may enforce their laws without exception for puberty blockers or hormone therapy. Changes downstream: State legislatures retain power to set eligibility rules for sex-separate school sports. Federal courts will defer to state definitions of biological sex in sports absent a constitutional violation (none shown here). Title IX regulations remain in force as they already authorize sex-separation.