United States
In the United States, child pornography is prohibited under both federal and state laws with some state laws including more or less restrictive definitions compared with federal law. Under federal law, child pornography is defined as visual depiction of minors (i.e. under 18) engaged in a sex act such as intercourse, oral sex, or ************ as well as the lascivious depictions of the genitals. Various federal courts in the 1980s and 1990s have concluded that "lewd" or "lascivious" depiction of the genitals does not require the genitals to be uncovered. Thus, for example, a video of underage teenage girls dancing erotically, with multiple close-up shots of their covered genitals, can be considered child porn.

Questions arose during the 1990s as to whether depictions of mere nudity of minors - such as those found in some nudist magazines and videos - were legal under federal child porn laws. A court case in 1999 determined that mere nudity involving minors does not come under the federal definition of child porn, nor does it necessarily qualify as obscene, as the Supreme Court had ruled previously that mere nudity in and of itself does not constitute obscenity. This ruling does not specifically address state laws, which may differ. For example, broader definitions in some states have created controversy when parents were arrested for taking photographs in which their small children were depicted nude during usual daily activities, such as bathing.

Further complicating the issue in the U. S. is that there is no clear legal definition in federal or state law as to what exactly constitutes a "lewd" or "lascivious" exhibition. In addition, these terms are often to be interpreted according to "contemporary community standards." Defining the standards of a community where residents come from a wide variety of ethnic and cultural backgrounds, and where moving from place to place is commonplace so that the nature of a community is continually changing, has proved extremely challenging.