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 Arkansas, the rules of civil procedure allow litigants to amend their pleadings, which include complaints, petitions, and answers. According to Arkansas Rule of Civil Procedure 15, a party may amend its pleading 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 their pleading only with the opposing party's written consent or the court's leave. The court should freely give leave when justice so requires. After a certain point in the proceedings, amendments may be more difficult to make and could be subject to stricter scrutiny by the court. At the federal level, Rule 15 of the Federal Rules of Civil Procedure provides similar allowances for amending pleadings, with the philosophy that cases should be decided on their merits rather than the technicalities of pleadings. However, amendments sought after certain timeframes or that would cause undue delay or prejudice to the other party may be denied.