Henry Cohen, Obscenity, Child Pornography, and Indecency: Brief Background and Recent Developments (CRS Report 98-670) (Oct. 6, 2009) (full-text).
The First Amendment provides that "Congress shall make no law ... abridging the freedom of speech, or of the press. . . ." The First Amendment applies, with two exceptions, to pornography, with that term being used to refer to any words or pictures of a sexual nature. The two exceptions are obscenity and child pornography; because these are not protected by the First Amendment, they may be, and have been, made illegal. Pornography and "indecent" material that are protected by the First Amendment may nevertheless be restricted in order to limit minors' access to them.