A grand jury is a type of jury, comprised of citizens who are presented with evidence from a state or federal prosecutor (District Attorney or United States Attorney) to determine whether there is probable cause to believe a person 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 defendant. This is known as a “true bill,” and the grand jury is said to have “returned a true bill.” If the grand jury does not believe there is sufficient evidence the accused committed a crime and should be put on trial, it is said to return a “no true bill" or "no bill."

The United States Constitution does not require states to use a grand jury to bring criminal charges against a person—but many states do use grand juries, and some states are required by their state constitution or statutes to use a grand jury to secure an indictment for any felony criminal offense. And the U.S. Supreme Court has interpreted the Constitution to require the federal government to use grand juries for all felony crimes.

Grand jury proceedings are not open to the public and accused persons and their attorneys do not have the right to appear before the grand jury, or to be informed of the proceedings. Witnesses subpoenaed by a grand jury do not have the right to have their attorney present during their testimony. The grand jury proceedings are generally transcribed by a court reporter, but the record is sealed.

Federal grand juries generally consist of 16-23 persons who serve or work on the grand jury for a few days each month for approximately one year—after which a new grand jury is selected by the Federal District Court. At least 12 jurors must agree to return a true bill for indictment of the accused person.

Procedures for the use of grand juries in the state court system vary from state to state and are generally governed by the state’s constitution, and statutes that are often located in the penal or criminal code, the code of criminal procedure, or the government code.

In Wisconsin, grand juries are not commonly used to bring charges against individuals. Instead, the state typically utilizes preliminary hearings where a judge determines if there is enough evidence to proceed to trial. However, Wisconsin law does allow for the use of grand juries. According to Wisconsin Statute § 968.02, a district attorney can request a judge to summon a grand jury. The grand jury in Wisconsin, like federal grand juries, operates in secrecy and is comprised of citizens who review evidence presented by the prosecutor to decide whether there is probable cause to believe a crime has been committed. If they find sufficient evidence, they issue a 'true bill,' leading to an indictment. If not, they return a 'no bill.' The proceedings are closed to the public, and the accused and their attorneys do not have the right to appear before the grand jury. Witnesses cannot have their attorneys present during testimony, and the records of the proceedings are sealed. The use of grand juries at the federal level is mandated for all felony crimes, as required by the Fifth Amendment of the U.S. Constitution, and federal grand juries consist of 16-23 members, with at least 12 needed to indict.