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 Connecticut, the rules governing the amendment of pleadings in civil lawsuits are outlined in the Connecticut Practice Book, which provides guidelines similar to the Federal Rules of Civil Procedure. A party to a civil lawsuit, whether a plaintiff or defendant, is generally allowed to amend their pleadings. This can include altering a complaint or petition to assert new claims or causes of action, or amending an answer to assert new defenses. The right to amend is subject to certain limitations, such as the timing of the amendment and the potential for prejudice to the opposing party. Amendments before trial are typically more freely granted, while those sought during trial may require stronger justification and can be subject to stricter scrutiny by the court. The court's discretion will often consider factors such as the need to avoid undue delay, prevent prejudice, or promote justice. Specific time frames and conditions for amendments are detailed in the Connecticut Practice Book, and parties are encouraged to consult these rules or an attorney for guidance on amending pleadings in their particular case.