The legal definition of obscenity is material that is patently offensive to the average person, applying contemporary community standards. This definition was established by the Supreme Court in the case of Miller v. California (1973).

The three-prong test for obscenity, established by the Supreme Court in Miller v. California (1973), requires that in order to be considered obscene, a work must meet all three of the following criteria: (1) Whether the average person, applying contemporary community standards, would find the work, taken as a whole, appeals to the prurient interest; (2) Whether the work depicts or describes, in a patently offensive way, sexual conduct specifically defined by the applicable state law; and (3) Whether the work, taken as a whole, lacks serious literary, artistic, political, or scientific value.

The First Amendment to the United States Constitution protects artistic expression from government censorship. This means that the government cannot censor or ban artistic works simply because they are considered to be obscene or offensive.

In Miller v. California (1973), the Supreme Court found that a film entitled "Carnal Knowledge" was obscene and could be banned from distribution. The Court held that the film met all three prongs of the obscenity test: it appealed to the prurient interest, it depicted sexual conduct in a patently offensive way, and it lacked serious literary, artistic, political, or scientific value.

In Memoirs v. Massachusetts (1966), the Supreme Court found that a book entitled "Fanny Hill" was not obscene and could not be banned from distribution. The Court held that the book did not meet the third prong of the obscenity test: it did not lack serious literary, artistic, political, or scientific value.