In a civil proceeding or criminal prosecution under the common law or under statute, a defendant may raise a defense (or defence)^[a] in an effort to avert civil liability or criminal conviction. A defense is put forward by a party to defeat a suit or action brought against the party, and may be based on legal grounds or on factual claims.^[2]

Besides contesting the accuracy of an allegation made against the defendant in the proceeding, the defendant may also make allegations against the prosecutor or plaintiff or raise a defense, arguing that, even if the allegations against the defendant are true, the defendant is nevertheless not liable. Acceptance of a defense by the court completely exonerates the defendant and not merely mitigates the liability.

The defense phase of a trial occurs after the prosecution phase, that is, after the prosecution "rests". Other parts of the defense include the opening and closing arguments and the cross-examination during the prosecution phase.

Since a defense is raised by the defendant in a direct attempt to avoid what would otherwise result in liability, the defendant typically holds the burden of proof. For example, a defendant who is charged with assault may claim provocation, but they would need to prove that the plaintiff had provoked the defendant.

In common law, a defendant may raise any of the numerous defenses to limit or avoid liability. These include:

• Lack of personal or subject matter jurisdiction of the court, such as diplomatic immunity. (In law, this is not a defense as such but an argument that the case should not be heard at all.)
• Failure to state a cause of action or other insufficiencies of pleading.
• Any of the affirmative defenses.
• Defenses conferred by statute – such as a statute of limitations or the statute of frauds.
• Ex turpi causa non oritur actio – the action against the defendant arises from an illegality.
• Volenti non fit injuria – consent by the victim or plaintiff.
• In pari delicto – both sides equally at fault.
• Act of God is an unforeseeable natural phenomenon which involves no human agency due directly to natural causes which cannot be foreseen.
• Necessity harm done to prevent a greater evil is not actionable even though the harm was caused intentionally.
• Mistake whether of fact or of law is no defence to action.
• The law permits use of reasonable force to protect one's person or property. If force is used for self-defence they will not be liable for harm.
• Unclean hands.

In addition to defenses against prosecution and liability, a defendant may also raise a defense of justification – such as self-defense and defense of others or defense of property.

In English law, one could raise the argument of a contramandatum, which was an argument that the plaintiff had no cause for complaint.^[3]

The defense in a homicide case may attempt to present evidence of the victim's character, to try to prove that the victim had a history of violence or of making threats of violence that suggest a violent character.^[4][5] The goal of presenting character evidence about the victim may be to make more plausible a claim of self-defense,^[4] or in the hope of accomplishing jury nullification in which a jury acquits a guilty defendant despite its belief that the defendant committed a criminal act.^[6]

Litigation is expensive and often may last for months or years. Parties can finance their litigation and pay for their attorneys' fees or other legal costs in a number of ways. A defendant can pay with their own money, through legal defense funds, or legal financing companies. For example, in the United Kingdom, a defendant's legal fees may be covered by legal aid.^[7]

• Absolute defense
• Lawsuit
• Legal defense fund
• Legal financing
• Self-defense
• Atturnato faciendo vel recipiendo

• Media related to Legal defenses at Wikimedia Commons