A grand jury is a group of citizens empowered by law to conduct legal proceedings, investigate potential criminal conduct, and determine whether criminal charges should be brought. It is separate from the courts, which do not preside over its functioning. The grand jury is so named because traditionally it has more jurors than a trial jury, sometimes called a petit jury. A grand jury in the United States is usually composed of 16 to 23 citizens, though in Virginia it has fewer members for regular or special grand juries.

The function of a grand jury is to accuse persons who may be guilty of a crime, but the institution is also a shield against unfounded and oppressive prosecution. It is a means for lay citizens, representative of the community, to participate in the administration of justice. The grand jury can also make presentments on crime and maladministration in its area. The grand jury acts as an investigative body, acting independently of either prosecuting attorney or judge. Criminal prosecutors present the case to the grand jury, attempting to establish probable cause to believe that a criminal offense has been committed. The grand jury may request that the court compel further evidence, including witness testimony and subpoenas of documents. All grand jury proceedings are conducted behind closed doors, without a presiding judge.

The grand jury focuses on preliminary criminal matters only and assesses evidence presented by a prosecutor to determine whether there is “probable cause” to believe an individual committed a crime and should be put on trial. If the grand jury determines there is enough evidence, an indictment will be issued against the individual. The grand jury proceedings are held in private, and the suspected criminal actor is usually not present at the proceedings. Unlike petit juries, grand juries do not meet every day, instead meeting in any number of calendar combinations throughout their term.