United States Magistrate Judges are appointed by the district judges and serve eight-year terms. Their duties are much like those of the district judges, except they do not have authority to try criminal cases, except misdemeanors. They can try civil cases by consent of the parties and do try a number of civil cases each year.
The United States Magistrate Judge system evolved from the United States commissioner system established in 1793. Congress conducted an exhaustive examination of the commissioner system in 1965, during which witnesses overwhelmingly favored overhauling the system and enhancing the positon. After hearings, Congress enacted legislation which replaced the position of "commissioner" with what is now that of "Magistrate Judge". As a result of that legislation, Magistrate Judges became judicial officers entrusted with expanded jurisdiction that authorizes them to handle a wider range of proceedings in civil and criminal cases.