The Comstock Law was a federal act passed by the United States Congress on March 3, 1873, as the Act for the "Suppression of Trade in, and Circulation of, Obscene Literature and Articles of Immoral Use". The Act criminalized usage of the U.S. Postal Service to send any of the following items:

In places like Washington D.C., where the federal government had direct jurisdiction, the act also made it a misdemeanor, punishable by fine and imprisonment, to sell, give away, or have in possession any "obscene" publication. Half of the states passed similar anti-obscenity statutes that also banned possession and sale of obscene materials, including contraceptives.

The law was named after its chief proponent, Anthony Comstock. Due to his own personal enforcement of the law during its early days, Comstock received a commission from the postmaster general to serve as a special agent for the U.S. Postal Services.