The First Amendment of the Constitution of the United States can provide a significant defense to alleged trademark infringement.

Fair use occurs when a descriptive mark is used in its primary, rather than secondary, meaning. For example, using Apple to describe the apple fruit would not infringe Apple, Inc.'s trademark "Apple." This is because such a use is purely descriptive and does not cause confusion with the secondary meaning of the mark.

The nominative fair use defense arises where a defendant has used the plaintiff's mark to describe the plaintiff's product, even if the defendant's ultimate goal is to describe his own product. Nominative fair use recognizes that occasionally, the need may arise to use a mark owned by someone else. The nominative fair use defense acknowledges that it is often virtually impossible to refer to a particular product for purposes of comparison, criticism, point of reference or any other such purpose without using the mark.

There are generally three requirements for the successful application of the nominative fair use defense. First, the service must be one not readily identifiable without use of the mark. Second, only so much of the mark may be used as is reasonably necessary. Finally, the user must refrain from actions that, in conjunction with the mark, suggest endorsement or sponsorship by the mark owner.

If one uses another party's trademark for a parody, and that use is not too directly tied to the mark's commercial use, there is no trademark infringement. Courts often balance the first amendment against trademark law . For example, the use of a character similar to a pig, named "Spam'am" in a Muppet movie was found to not infringe Hormel's "Spam" trademark. The parody defense is generally more fact based and can also involve a likelihood of confusion analysis.