To describe progression, content, and stringency of state legislation regulating indoor tanning and association with state government political party leadership. Trained research assistants used legal mapping methods to code legislative bills on indoor tanning introduced in US states, the District of Columbia, and Puerto Rico. We calculated composite scores on the stringency of age restrictions and of warnings, operator requirements, and enforcement. We evaluated associations of the political party of the legislative sponsor and legislature majority. Between 1992 and 2023, 184 bills were introduced in 49 of 50 states and DC (56 laws were enacted, and 126 bills failed). An under-18 ban was enacted in 22 states and DC. Party affiliation of the bill sponsor and legislature majority combined to affect bill passage and age restrictions. In many states, it took several years and proposed bills before a law on indoor tanning was enacted. Enacted bills were more stringent than failed bills. Increasing support for stringent regulations on indoor tanning is evident and may motivate other states or the federal government to prohibit minors from using indoor tanning facilities. (. 2025;115(2):191-200. https://doi.org/10.2105/AJPH.2024.307894).