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 Florida, grand juries are used in accordance with both state law and the federal legal system. Under the Florida Constitution and the Florida Rules of Criminal Procedure, a grand jury is convened to determine whether there is probable cause to believe that a person has committed a crime that is punishable by death or life imprisonment. Florida grand juries consist of 15 to 21 members, and at least 12 members must concur to issue an indictment or 'true bill.' If the grand jury finds insufficient evidence, they return a 'no true bill.' Grand jury proceedings in Florida are secret, and neither the accused nor their attorneys have the right to be present or informed about the proceedings. Witnesses are not allowed to have their attorneys present during testimony. The federal system, which also operates in Florida, requires the use of grand juries for all felony offenses, with grand juries consisting of 16 to 23 members. In the federal system, at least 12 jurors must agree to indict. The federal grand jurors serve for about one year and meet periodically. The specific procedures and requirements for grand juries in Florida are detailed in the state's statutes and rules of criminal procedure.