In the common law, a grand jury is a type of jury that determines whether there is enough evidence for a trial. Grand juries carry out this duty by examining evidence presented to them by a prosecutor and issuing indictments, or by investigating alleged crimes and issuing presentments. A grand jury is traditionally larger than and distinguishable from a petit jury, which is used during a trial.

History

The first instance of a grand jury can be traced back to the Assize of Clarendon, an 1166 act of Henry II of England. In fact, Henry's chief contribution to the development of the English monarchy was to increase the jurisdiction of the royal courts at the expense of the feudal courts. Itinerant justices on regular circuits were sent out once each year to enforce the "King's Peace." To make this system of royal criminal justice more effective, Henry employed the method of inquest used by William the Conqueror in the Domesday Book. In each shire a body of important men were sworn (jure) to report to the sheriff all crimes committed since the last session of the circuit court. Thus originated the modern grand jury that presents information for an indictment. The grand jury was later recognized by King John in the Magna Carta in 1215 on demand of the nobility.

In the early decades of the United States grand juries played a major role in public matters. During that period counties followed the traditional practice of requiring all decisions be made by at least 12 of the grand jurors, so that for a size of 23 a bare majority would be 12. Any citizen could bring a matter before it directly, from a public work that needed repair, to a delinquent official, to a complaint of a crime, and they could conduct their own investigations. In that era most criminal prosecutions were conducted by private parties, either a law enforcement officer, a lawyer hired by a crime victim or his family, or even by laymen, who could bring a bill of indictment to the grand jury, and if the grand jury found there was sufficient evidence for a trial, that the act was a crime under law, and that the court had jurisdiction, then by returning the indictment to the complainant, it appointed him to exercise the authority of an attorney general, that is, one having a general power of attorney to represent the state in the case. The grand jury served to screen out incompetent or malicious prosecutions. The advent of official public prosecutors in the later decades of the 19th century largely displaced private prosecutions, but also led to their capturing grand juries and using them in ways for which they were not originally intended.

In Ireland grand juries were active from medieval times in the English-controlled parts of the island, mainly functioning as local government authorities at the county level, as well as having a pre-trial judicial function for serious criminal cases. Members were usually wealthy landowners, farmers and merchants, who selected new members. From 1691 to 1793 Roman Catholics were excluded from membership. They were replaced by democratically-elected County Councils by the Act of 1898.cn: date=July 2008