A lawsuit is started by filing by a Complaint. The party filing the Complaint is called the Plaintiff. In certain cases, a Plaintiff may decide to change his initial Complaint. There are many possible reasons that a Plaintiff may change or "amend" the Complaint (ie. the discovery of new evidence, a change in law, or even correcting a simple mistake). Federal Courts have specific rules for amending a Complaint. A Plaintiff may amend her Complaint once any time before an Answer or "responsive pleading" is served. Fed. R. Civ. P.15(a). However, if the amendment is sought after the Answer is filed, the Plaintiff must either obtain (i) written consent from the opposing party or (ii) permission from the Court.

Fortunately, that permission or "leave", as it is referred to in the rules, is usually freely given. In fact, under the rules, it would be inappropriate for the Court to deny the request so long as there has been no undue delay, bad faith, or dilatory motive on the part of the movant, nor undue prejudice to the non-moving party. An example of "undue prejudice" would be if the Court concluded that the Plaintiff was seeking to amend the Complaint merely to delay the trial or add claims that the defendant would not have time to test in discovery.

Federal Courts have recognized the generous standard in Rule 15 (a). In fact the United States Supreme Court has declared that the purpose of this policy is primarily because the Courts favor giving a Plaintiff the opportunity to "test his claim on the merits" Foman v. Davis, 371 U.S. 178, 182 (1962). In other words, a party should be given his "day in Court", rather than limiting Plaintiffs claims through overly restrictive pleading rules.