Rule 15 of the Federal Rules of Civil Procedure governs the process of amending pleadings in civil litigation. This rule allows parties to modify their pleadings under certain circumstances, which is essential for ensuring that cases are decided based on the merits rather than procedural technicalities. Amendments can be made both as a matter of course and with permission from the court, and they can include adding new claims or defenses, correcting inaccuracies, or substituting parties.