Although Federal courts generally look to State law to determine the limitations period for a federally created right that has no federally specified limitations period, the courts will look to Federal law to determine when the period begins. Under the Federal doctrine of fraudulent concealment, the statutory limitations period will begin to run when the cause of action is discovered, or should have been discovered, by the exercise of due diligence. What one must plead and show to establish fraudulent concealment depends on the circumstances of each case. In actions not based on fraud, the plaintiff must plead with particularity and show (1) fraudulent concealment by the defendant; (2) the ignorance of the plaintiff as to the cause of action prior to the running of the limitations period before the commencement of the suit; and (3) that once on notice of the possible cause of action, the plaintiff exercised due diligence in discovering the facts of the claim. In actions based on fraud, the plaintiff need not plead fraudulent concealment if the concealment claim is based on the substantive fraud because the defendant is on notice of the fraud claim. When the defendant claims that the statute of limitations bars the suit, the plaintiff must establish the last two aforementioned elements. If the concealment does not involve the substantive fraud, the plaintiff must establish all three elements. For all types of cases, leave to amend is liberally granted with few exceptions. A total of 175 footnotes are listed. For additional material on RICO, see NCJ 78839. (Author summary modified)