A grand jury is a legal body that is empowered to conduct official proceedings to investigate potential criminal conduct and to determine whether criminal charges should be brought. A grand jury may compel the production of documents and may compel the sworn testimony of witnesses to appear before it. A grand jury is separate from the courts, which do not preside over its functioning.
Currently, only the United States retains grand juries, although some other common law jurisdictions formerly employed them, and most other jurisdictions employ some other type of preliminary hearing. Grand juries perform both accusatory and investigatory functions. The investigatory functions of the grand jury include obtaining and reviewing documents and other evidence and hearing the sworn testimony of witnesses that appear before it. The grand jury's accusatory function is to determine whether or not there is probable cause to believe that one or more persons committed a certain offense within the venue of the district court. The "grand jury" in the United States is composed of 16 to 23 citizens. In Ireland, they also functioned as local government authorities.
A grand jury is so named because traditionally it has a greater number of jurors than a trial jury, also known as a petit (French for small) jury or, in English usage the spelling can be petty jury.
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 effect on 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 was sworn (juré) 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 Magna Carta in 1215 on demand of the nobility.
England and Wales
The sheriff of every county was required to return to every quarter sessions and assizes (or more precisely the commission of oyer and terminer and of gaol delivery), 24 men of the county "to inquire into, present, do and execute all those things which, on the part of our Lady the Queen, shall then be commanded them". Grand jurors at the assizes or at the borough quarter sessions did not have property qualifications; but, at the county quarter sessions, they had the same property qualification as petty jurors. However, at the assizes, the grand jury generally consisted of gentlemen of high standing in the county.
After the court was opened by the crier making proclamation, the names of those summoned to the grand jury were called and they were sworn. They numbered at least 12 and not more than 23. The person presiding (the judge at the assizes, the chairman at the county sessions, the recorder at the borough sessions) gave the charge to the grand jury, namely he directed their attention to points in the various cases about to be considered which required explanation.
The charge having been delivered, the grand jury withdrew to their own room, having received the bills of indictment. The witnesses whose names were endorsed on each bill were sworn as they come to be examined, in the grand jury room, the oath being administered by the foreman, who wrote his initials against the name of the witness on the back of the bill. Only the witnesses for the prosecution were examined, as the function of the grand jury is merely to inquire whether there is sufficient ground to put the accused on trial. If the majority of them (and at least 12) thought that the evidence so adduced made out a sufficient case, the words "a true bill" were endorsed on the back of the bill. If they were of the opposite opinion, the phrase "not a true bill," or the single Latin word "ignoramus" ("we do not know" or "we are ignorant of"), was endorsed instead and the bill was said to be ignored or thrown out. They could find a true bill as to the charge in one count, and ignore that in another; or as to one defendant and not as to another; but they could not, like a petty jury, return a special or conditional finding, or select part of a count as true and reject the other part. When some bills were "found", some of jurors came out and handed the bills to the clerk of arraigns (in assizes) or clerk of the peace, who announced to the court the name of the prisoner, the charge, and the endorsements of the grand jury. They then retired and considered other bills until all were disposed of; after which they were discharged by the aforementioned judge, chairman, or recorder.
If a bill was thrown out, although it could not again be preferred to the grand jury during the same assizes or sessions, it could be preferred at subsequent assizes or sessions, but not of course in respect of the same offence if a petty jury had returned a verdict.
Ordinarily, bills of indictment were preferred after there had been an examination before the magistrates. But this need not always take place. With certain exceptions, any person could prefer a bill of indictment against another before the grand jury without any previous inquiry into the truth of the accusation before a magistrate. This right was at one time universal and was often abused. A substantial check was put on this abuse by the Vexatious Indictments Act 1859. This Act provided that for certain offences which it listed (perjury, libel, etc.), the person presenting such an indictment must be bound by recognizance to prosecute or give evidence against the accused, or alternatively had judicial permission (as specified) so to do.
If an indictment was found in the absence of the accused, and he/she was not in custody and had not been bound over to appear at assizes or sessions, then process was issued to bring that person into court, as it is contrary to the English law to try an indictment in the absence of the accused.
The grand jury's functions were gradually made redundant by the development of committal proceedings in magistrates courts from 1848 onward when the (three) Jervis Acts, such as the Justices Protection Act 1848, codified and greatly expanded the functions of magistrates in pre-trial proceedings; these proceedings developed into almost a repeat of the trial itself. The grand jury ceased in 1933 to function in England with the Administration of Justice (Miscellaneous Provisions) Act 1933 and was entirely abolished in 1948, when a clause from 1933 saving grand juries for offences relating to officials abroad was repealed by the Criminal Justice Act 1948.
The Grand Jury was introduced in Scotland, solely for High Treason, by an Act of the Parliament of Great Britain, a year after the union with England, by the Treason Act 1708. Section III of the Act required the Scottish courts to try cases of treason and misprision of treason according to English rules of procedure and evidence. This rule was repealed in 1945.
The first grand jury that sat under the British treason act met at Edinburgh on 10 October 1748 to take cognisance of the charges against such rebels as had not surrendered, following the Jacobite rising of 1745.
An account of its first use in Scotland illustrates the institution's characteristics. It consisted of 23 good and lawful men, chosen out of 48 who were summoned; 24 from the county of Edinburgh (Midlothian), 12 from Haddington (East Lothian) and 12 from Linlithgow (West Lothian). The court consisted of three judges from the High Court of Justiciary (Scotland's highest criminal court), of whom Tinwald (Justice Clerk) was elected preses (presiding member). Subpoenas under the seal of the court and signed by the clerk were executed on a great number of persons in different shires, requiring them to appear as witnesses under the penalty of £100 each. The preses named Sir John Inglis of Cramond as Foreman of the Grand Jury, who was sworn first in the English manner by kissing the book, the others followed by three at a time; after which his lordship, addressing the jurors, informed them that the power His Majesty's advocate possessed before the union, of prosecuting any person for high treason, who appeared guilty on a precognition taken of the facts, being now done away, that power was lodged with them, a grand jury, 12 of whom behoved to concur before a true bill could be found. An indictment was then preferred in court and the witness endorsed on it were called over and sworn; on which the jury retired to the exchequer chambers and the witnesses were conducted to a room near it, whence they were called to be examined separately. Two solicitors for the crown were present at the examination but no-one else; and after they had finished and the sense of the jury was collected, the indictment was returned a "true bill", if the charges were found proved, or "ignoramus" if doubtful. The proceedings continued for a week, in which time, out of 55 bills, 42 were sustained and 13 dismissed.
Further Acts of Parliament in 19th Century regarding Treason did not specify this special procedure and the Grand Jury was used no longer.
In Ireland, grand juries were active from the Middle Ages during the Lordship of Ireland in parts of the island under the control of the English government (The Pale), that was followed by the Kingdom of Ireland. They mainly functioned as local government authorities at the county level. The system was so-called as the grand jurors had to present their public works proposals and budgets in court for official sanction by a judge. Grand jurors were usually the largest local payers of rates, and therefore tended to be the larger landlords, and on retiring they selected new members from the same background.
Distinct from their public works function, as property owners they also were qualified to sit on criminal juries hearing trials by jury, as well as having a pre-trial judicial function for serious criminal cases. Many of them also sat as magistrates judging the less serious cases.
They were usually wealthy "country gentlemen" (i.e. landowners, landed gentry, farmers and merchants):
A country gentleman as a member of a Grand Jury...levied the local taxes, appointed the nephews of his old friends to collect them, and spent them when they were gathered in. He controlled the boards of guardians and appointed the dispensary doctors, regulated the diet of paupers, inflicted fines and administered the law at petty sessions.
From 1691 to 1793, Dissenters and Roman Catholics were excluded from membership. The concentration of power and wealth in a few families caused resentment over time. The whole local government system started to become more representative from the passing of the Municipal Corporations (Ireland) Act 1840. Grand juries were replaced by democratically-elected County Councils by the Local Government (Ireland) Act 1898, as regards their administrative functions.
After the formation of Irish Free State in 1922, grand juries was not required, but they persisted in Northern Ireland until abolished by the Grand Jury (Abolition) Act of the Parliament of Northern Ireland in 1969.
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 twelve of the grand jurors, (e.g., for a twenty-three-person grand jury, twelve people would constitute a bare majority). Any citizen could bring a matter before a grand jury directly, from a public work that needed repair, to the delinquent conduct of a public official, to a complaint of a crime, and grand juries 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. A layman could bring a bill of indictment to the grand jury; 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, it would return the indictment to the complainant. The grand jury would then appoint the complaining party 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.
While all states currently have provisions for grand juries, today approximately half of the states employ them and twenty-two require their use, to varying extents. The constitution of Pennsylvania required, between 1874 and 1968, that a grand jury indict all felonies (see Article 1, section 10).
Grand juries were once common across Canada. The institution of British civil government in 1749 at Nova Scotia brought the judicature system peculiar to that form, and the Grand Jury was inherent to it. A similar form derived in Quebec from the promise of the Royal Proclamation of 1763 that a faithful copy of Laws of England would be instituted in the North American possessions of the Crown. Archival records are found that document the presentments of a Grand Jury in Quebec as early as 16 October 1764. One of the chief complaints was related to the jury trial, and the use of language. The desire for English law was a driver for the division in 1791 of Quebec, as it was then known, at the Ottawa river into Upper Canada and Lower Canada, as each of the two groups (French and English) desired to maintain their traditions. In point of fact, the second law passed in Upper Canada relates to (petit) jury trial. This was continued so that Chapter 31 of the 1859 Consolidated Statutes of Upper Canada specifies the constitution of Grand and Petit Juries in the province (now known as Ontario). The colony at St. John's Island, ceded by France in 1763, and separated on 30 May 1769 from Nova Scotia, became Prince Edward Island on 29 November 1798. PEI derived its grand jury from its administrative parent between 1763 and 1769, Nova Scotia, as did Sunbury County when it was split off in 1784 to become the Colony of New Brunswick. The Colony of British Columbia, when it was formed on 2 August 1858, instituted a grand jury, along with the Colony of the Queen Charlotte Islands (1853-1863) and the Colony of Vancouver Island (1848-1866) when the latter were absorbed by the former.
Old courthouses with the two jury boxes necessary to accommodate the 24 jurors of a grand jury can still be seen. The grand jury would evaluate charges and return what was called a "true bill (of indictment)" if the charges were to proceed. or a verdict of nolle prosequi if not. The practice gradually disappeared in Canada over the course of the twentieth century, after being the subject of extended discussions late in the 19th. It was ultimately abolished in 1984 when the Nova Scotia courts formally ended the practice. PEI maintained a grand jury as recently as 1871.
The grand jury existed in New South Wales for a short period in the 1820s, but it was discontinued by the new Constitution Act of 1828. However, in South Australia and Western Australia, grand juries existed for longer periods of time. In South Australia, the first Grand Jury sat on 13 May 1837, but it was abolished in 1852. In Western Australia, by the Grand Jury Abolition Act Amendment Act 1883 (WA), the Grand Jury was abolished (section 4: A Grand Jury shall not be summoned for the Supreme Court of Western Australia, nor for any General Quarter Sessions for the said Colony).
The Australian state of Victoria maintained, until 2009, provisions for a grand jury in the Crimes Act 1958 under section 354 indictments, which had been used on rare occasions by individuals to bring other persons to court seeking them to be committed for trial on indictable offences. Grand juries were introduced by the Judicature Act 1874 and have been used on a very limited number of occasions. Its function in Victoria particularly relates to alleged offences either by bodies corporate or where magistrates have aborted the prosecution.
Trial by Jury was introduced in the Cape Colony by Richard Bourke, Lieutenant Governor and acting Governor of the colony between 1826-28. The acting Governor, who was later influential in the establishment of jury trial in New South Wales, obtained the consent of the Secretary of State for the Colonies in August 1827 and the first Charter of Justice was issued on 24 August 1827 
Jury trial was brought into practical operation in 1828 and the 1831 Ordinance 84 laid down that criminal cases would be heard by a panel of nine, selected from males aged between 21 and 60, owning or renting property to a value of £1:17 shillings per annum or having liability for taxes of 30 shillings in Cape Town and 20 shillings outside the town. Black (i.e. non-white) jurors were not entirely excluded and sat occasionally. This is not to imply, however, that juries did not operate in an oppressive manner towards the Black African and Asian residents of the Cape, whose participation in the jury lists was, in any event, severely limited by the property qualification. The property qualification was amended in 1831 and 1861 and, experimentally, a grand jury came into operation.
The Grand Jury was established for Cape Town alone. It met quarterly. In 1842 it was recorded  that it served a district of 50,000 inhabitants and in one quarterly session there were six presentments (1 homicide, 2 assaults, 1 robbery, 1 theft, 1 fraud).
As elsewhere, the judge could use his charge to the Grand Jury to bring matters of concern to him to the attention of the public and the government. In May 1879 Mr. Justice Fitzpatrick, returning from Circuit in the northern and western parts of Cape Colony, gave a charge to the Grand Jury at the Criminal Sessions at Cape Town, in which, after congratulating them upon the lightness of the calendar, he observed there were indications in the country of a growing mutual bad feeling between the races, etc. This was reported in the Cape Argus and was a subject of a question to the government in the House of Commons in London 
Grand Juries were established in France in 1791 under the name jury d'accusation, but they were abolished with the introduction of the Code Napoleon in 1808. During this period they also operated in Belgium  from 1795, which was divided into French departements in October 1795.
The jury law of 1791 created an eight man jury d'accusation in each arrondissement (a subdivision of the departement) and a twelve man jury de jugement in each departement. In each arrondissement the procureur-syndic drew up a list of 30 jurors from the electoral roll every three months for the jury d'accusation. There was no public prosecutor or juge d'instruction. Instead the police or private citizens could bring a complaint to the Justice of the Peace established in each canton (a subdivision of the arrondissement). This magistrate interrogated the accused to determine whether grounds for prosecution existed and if so sent the case to the directeur du jury (the director of the jury d'accusation), who was one of the arrondissement's civil court judges, and who served in the post for six months on a rotating basis. He decided whether to dismiss the charges or, if not, whether the case was a délit (misdemeanour) or a crime (felony, i.e. imprisonable for 2 years or more). Délits went to the tribunal de police correctionnelle of the arrondissement, while for crimes the directeur de jury convoked the jury d'accusation of the arrondissement, in order to get an indictment. The directeur du jury drew up the bill of indictment (act d'accusation) summarising the charges to be presented to the jury d'accusation. The directeur made a presentation to the jury in the absence of the accused and the jury heard the witnesses. The jury then decided by majority vote whether there were sufficient grounds for the case to go to the tribunal criminel of the departement. Between 1792-5 there was no property qualification for jurors.
The functions of the jury d’accusation were prescribed in the law of 1791 passed by the Constituent Assembly and were maintained and re-enacted in the Code des Délits et des Peines of 3 Brumaire, Year 4 (25 October 1795) and this was the operative law until it was abolished in 1808. Special juries and special grand juries were originally defined in law, for cases thought to require more qualified jurors, but these were abolished in Year 8 (1799) 
- Inquests in England and Wales
- Committal procedure
- Immunity from prosecution
- Counties of Ireland
- Civil grand jury
- 112 S.Ct. 1735 504 U.S. 36 118 L.Ed.2d 352 UNITED STATES, Petitioner v. John H. WILLIAMS, Jr. No. 90-1972. Argued Jan. 22, 1992. Decided May 4, 1992
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- Stokes, Mary: "Grand Juries and ‘Proper Authorities’: Low Law, Soft Law and Local Governance in Canada West/Ontario, 1850-1880"
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- The California Grand Jurors' Association
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- Who invented the grand jury? from the Straight Dope
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- Grand Juries
- The Grand Jury, Hugh Turley, Hyattsville Life and Times, January, 2007
- Grand juror handbooks from the court system
- U.S. Federal Grand Jury Handbook (PDF)
- Handbook for Hennepin County (Minnesota) Grand Jurors (PDF)