A grand jury is a jury—a group of citizens—empowered by law to conduct legal proceedings, investigate potential criminal conduct, and determine whether criminal charges should be brought. A grand jury may subpoena physical evidence or a person to testify. A grand jury is separate from the courts, which do not preside over its functioning.
The United States and Liberia are the only countries that retain grand juries, though other common law jurisdictions formerly employed them, and most others now employ a differing procedure that does not involve a jury: a preliminary hearing. Grand juries perform both accusatory and investigatory functions. The investigatory functions of grand juries include obtaining and reviewing documents and other evidence, and hearing sworn testimonies of witnesses who appear before it; the accusatory function determines whether there is probable cause to believe that one or more persons committed a particular offense within the venue of a district court.
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. In Ireland, they also functioned as local government authorities. In Japan, the Law of July 12, 1948, created the Kensatsu Shinsakai (Prosecutorial Review Commission or PRC system), inspired by the American system.