Copyright misuse is an equitable defense against copyright infringement in the United States based on the unreasonable conduct of the copyright owner.
The doctrine forbids the copyright owner from attempting to secure an exclusive right or limited monopoly (usually through restrictive licensing practices) that is not granted by federal copyright law and is contrary to public policy. Finding that a copyright owner has engaged in misuse prevents the owner from enforcing his copyright through the securing of an injunction until he has "purged" himself of the misuse—i.e., ceased the restrictive practices.
Copyright misuse is not a defense recognized in the provisions of the federal Copyright Act, but is instead purely founded in federal case law, beginning with a 1990 case in the Fourth Circuit. The doctrine is derived from the longstanding equitable doctrine of "unclean hands", which bars a party from asking for equitable relief (such as an injunction) against another when they have themselves acted improperly (though not necessarily illegally). Copyright misuse is analogous to the concept of patent misuse.
Recently, there have been cases of use of the DMCA to prevent interoperability with devices such as garage door openers and ink cartridges to which copyright does not apply.