The Comstock Law was a 19th century United States law that made it illegal to send any "obscene, lewd, or lascivious" books through the mail. It was passed on March 3, 1873 and is a clear example of censorship. It was named after its chief proponent, the anti-obscenity crusader Anthony Comstock. The enthusiastic enforcement of the Act, often by Comstock himself, made American censorship notorious in Europe. George Bernard Shaw, who had his own works censored in the United States, coined the word "comstockery" to describe censorship without regard for culture or merit.

The Comstock Law not only targeted pornography as such, but also all contraceptive equipment and descriptions of contraceptive methods.

Comstock Law states: Be it enacted… That whoever, within the District of Columbia or any of the Territories of the United States…shall sell…or shall offer to sell, or to lend, or to give away, or in any manner to exhibit, or shall otherwise publish or offer to publish in any manner, or shall have in his possession, for any such purpose or purposes, an obscene book, pamphlet, paper, writing, advertisement, circular, print, picture, drawing or other representation, figure, or image on or of paper of other material, or any cast instrument, or other article of an immoral nature, or any drug or medicine, or any article whatever, for the prevention of conception, or for causing unlawful abortion, or shall advertise the same for sale, or shall write or print, or cause to be written or printed, any card, circular, book, pamphlet, advertisement, or notice of any kind, stating when, where, how, or of whom, or by what means, any of the articles in this section…can be purchased or obtained, or shall manufacture, draw, or print, or in any wise make any of such articles, shall be deemed guilty of a misdemeanor, and on conviction thereof in any court of the United States…he shall be imprisoned at hard labor in the penitentiary for not less than six months nor more than five years for each offense, or fined not less than one hundred dollars nor more than two thousand dollars, with costs of court.

The Comstock Law prohibition of birth control was not overturned until U.S. v. One Package of Japanese Pessaries in 1936.