The rules of civil procedure or the code of civil procedure in state and federal courts usually permit a party to a civil lawsuit (a litigant) to amend its pleadings.

A plaintiff can amend the complaint or petition to assert new claims or causes of action before or during trial, subject to certain limitations—and the defendant can amend the answer to the lawsuit to assert new defenses to the plaintiff's claims before or during trial, subject to certain limitations.

In Georgia, the rules of civil procedure allow litigants to amend their pleadings, which include complaints, petitions, and answers. Under the Georgia Civil Practice Act, specifically O.C.G.A. § 9-11-15, a party may amend its pleadings once as a matter of course before a responsive pleading is served or, if the pleading is one to which no responsive pleading is permitted and the action has not been placed upon the trial calendar, the party may so amend it within 30 days after it is served. Otherwise, a party may amend its pleadings only by leave of court or by written consent of the adverse party; leave shall be freely given when justice so requires. At the federal level, Rule 15 of the Federal Rules of Civil Procedure similarly allows parties to amend their pleadings, with the court's leave, and such leave should be freely given when justice requires. There are limitations to these amendments, such as timing and the potential for prejudice to the opposing party, and in some cases, amendments may not be allowed if they would result in undue delay or would be futile.