A bathroom bill is the common name for legislation that defines access to public toilets and other sex-segregated facilities by a person's sex or gender identity. Depending on how a jurisdiction defines "sex," such laws can either affirm transgender people's right to use facilities matching their gender identity or restrict them to facilities matching their sex assigned at birth. Most modern bathroom bills fall into the latter category, requiring individuals to use restrooms, locker rooms, and changing facilities corresponding to the sex listed on their original birth certificate.

Proponents argue these laws protect privacy, modesty, and safety, and guard against voyeurism or assault in shared facilities. Critics, including major medical and psychological associations, argue that such laws do not make cisgender people safer while increasing risks and psychological harm for transgender people. Researchers, including UCLA's Williams Institute, have found no significant increase in bathroom-related crimes following the passage of transgender-inclusive nondiscrimination protections.

The modern wave of U.S. bathroom bills traces back to a 2013 Colorado case allowing a transgender child to use the girls' restroom at her school, and gained national attention with North Carolina's 2016 "HB2" law, which prompted a wide business and entertainment boycott before being partially repealed. Momentum for such bills resurged in the mid-2020s, with numerous states enacting restrictions covering government buildings, schools, and in some cases private facilities. Penalties for violations vary by state and can include criminal misdemeanor charges, civil lawsuits, and loss of state funding for noncompliant institutions.