In the law of the United States, a special master is generally a subordinate official appointed by a judge to make sure that judicial orders are actually followed, or in the alternative, to hear evidence on behalf of the judge and make recommendations to the judge as to the disposition of a matter. The special master should not be confused with the traditional common law concept of a master, a judge of the High Court entrusted to deal with summary and administrative matters falling short of a full trial.
In the federal judiciary of the United States, a special master is an adjunct to a federal court. Rule 53 of the Federal Rules of Civil Procedure allows a federal court to appoint a master, with the consent of the parties, to conduct proceedings and report to the Court.
The role of the special master (who is frequently, but not necessarily, an attorney) is to supervise those falling under the order of the court to make sure that the court order is being followed, and to report on the activities of the entity being supervised in a timely matter to the judge or the judge's designated representatives. Special masters have been controversial in some cases, and are often cited by critics as an example of judicial supremacy over the other branches of government. For example, at times they have ordered the expenditure of funds over and above the amount appropriated by a legislative body for the remediation of the situation being examined. To this point, their powers have generally been found to be valid and their remedies upheld by United States courts.
The United States Supreme Court will normally assign original jurisdiction disputes (cases such as disputes between states that are first heard at the Supreme Court level) to a special master to conduct what amounts to a trial court (the taking of evidence and a ruling). The Supreme Court can then assess the master's ruling much as a normal appeals court would, rather than conduct the trial itself. This is necessary as trials in the U.S. almost always involve live testimony and it would be too unwieldy for nine justices to rule on evidentiary objections in real time.