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 Rhode Island, as in other jurisdictions, the rules of civil procedure allow litigants to amend their pleadings, which include complaints, petitions, and answers. According to the Rhode Island Rules of Civil Procedure, specifically Rule 15, a party may amend its pleading once as a matter of course within 20 days after it is served, or if the pleading is one to which a responsive pleading is required, 20 days after service of the responsive pleading or service of a motion under Rule 12(b), (e), or (f), whichever is earlier. Beyond this, amendments require either consent from the opposing party or leave from the court, which the court should freely give when justice so requires. This is to ensure that all claims and defenses can be fully and fairly adjudicated. However, the court may deny an amendment if it finds reasons such as undue delay, bad faith, dilatory motive, repeated failure to cure deficiencies by amendments previously allowed, undue prejudice to the opposing party, or futility of the amendment. At the federal level, the Federal Rules of Civil Procedure provide similar provisions under Rule 15, allowing for amendments to pleadings with the court's discretion to permit such changes in the interest of justice and to facilitate a decision on the merits rather than on technicalities.