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 North Carolina, the rules governing the amendment of pleadings in civil lawsuits are found in the North Carolina Rules of Civil Procedure. Rule 15 allows a party to amend its pleadings, and it is generally liberal in permitting such amendments. 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, the party may amend it within 30 days after it is served. Otherwise, a party may amend its pleading only by leave of court or by written consent of the adverse party, and leave shall be freely given when justice so requires. This rule is designed to ensure that cases are decided on their merits rather than on technicalities. At the federal level, the Federal Rules of Civil Procedure Rule 15 similarly allows parties to amend their pleadings, and courts are instructed to freely give permission to amend when justice requires. Both state and federal rules also contain provisions for amending pleadings to add counterclaims, crossclaims, or third-party claims. However, there are limitations, such as time restrictions and the potential prejudice to the opposing party, which the court will consider when deciding whether to grant leave to amend.