A victimless crime is an illegal act that typically either directly involves only the perpetrator or occurs between consenting adults. Because it is consensual in nature, whether there involves a victim is a matter of debate. Definitions of victimless crimes vary in different parts of the world and different law systems, but usually include possession of any illegal contraband, recreational drug use, prostitution and prohibited sexual behavior between consenting adults, assisted suicide, and smuggling among other similar infractions.

In politics, a lobbyist or an activist might use the term victimless crime with the implication that the law in question should be abolished.

Victimless crimes are, in the harm principle of John Stuart Mill, "victimless" from a position that considers the individual as the sole sovereign, to the exclusion of more abstract bodies such as a community or a state against which criminal offenses may be directed. They may be considered offenses against the state rather than society.