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 Missouri, grand juries play a crucial role in the criminal justice system for serious offenses. They are composed of citizens who review evidence presented by a prosecutor to determine if there is probable cause to believe that a crime has been committed and whether a trial should be held. If the grand jury finds sufficient evidence, it issues an indictment, known as a 'true bill.' Conversely, if they find the evidence lacking, they return a 'no true bill.' While the U.S. Constitution does not mandate states to use grand juries, Missouri law does require their use for felony charges. Grand jury proceedings in Missouri are secretive; they are not open to the public, and the accused and their attorneys do not have the right to be present or informed about the proceedings. Witnesses cannot have their attorneys with them during testimony. The proceedings are recorded but kept sealed. The size of a federal grand jury ranges from 16 to 23 members, and at least 12 must concur to indict. Missouri's specific procedures for grand juries are governed by state statutes and can be found in the state's criminal or procedural codes.