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. Grand juries are separate from the courts, which do not preside over their functioning. They are named "grand" because they traditionally have more jurors than a trial jury, which is sometimes called a petit jury. In the United States, a grand jury 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. Grand juries can also make presentments on crime and maladministration in their 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. If the grand jury determines there is enough evidence, an indictment will be issued against the individual.

Grand juries are used for preliminary criminal matters only and assess 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. Unlike petit juries, grand juries do not meet every day, instead meeting in any number of calendar combinations throughout their term. Grand jury proceedings are private, and the suspected criminal actor is usually not present at the proceedings. The grand jury is generally free to pursue its investigations unhindered by external influence or supervision.

In summary, 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. They are separate from the courts, and their function is to accuse persons who may be guilty of a crime. Grand juries act as an investigative body, acting independently of either prosecuting attorney or judge, and their proceedings are private.