In civil lawsuits, affirmative defenses include the statute of limitations, the statute of frauds, waiver, and other affirmative defenses such as, in the United States, those listed in Rule 8 (c) of the Federal Rules of Civil Procedure.
In an affirmative defense, the defendant may concede that they committed the alleged acts, but they prove other facts which, under the law, either justify or excuse their otherwise wrongful actions, or otherwise overcomes the plaintiff's claim.
[4] Consequently, affirmative defenses limit or excuse a defendant's criminal culpability or civil liability.
[citation needed] Among the most controversial affirmative defenses is the insanity defense,[8] whereby a criminal defendant seeks to be excused from criminal liability on the ground that a mental illness, at the time of the alleged crime, prevented him or her from understanding the wrongful nature of his or her actions.
Rule 8(c) specifically enumerates the following defenses: "accord and satisfaction, arbitration and award, assumption of risk, contributory negligence, discharge in bankruptcy, estoppel, failure of consideration, fraud, illegality, injury by fellow servant, laches, license, payment, release, res judicata, statute of frauds, statute of limitations, waiver, and any other matter constituting an avoidance or affirmative defense."
[10] In Campbell v. Acuff-Rose Music, Inc.,[11] the United States Supreme Court held that fair use was an affirmative defense to copyright infringement.