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 New Hampshire, grand juries play a role similar to that in other states and the federal system, where they are used to determine whether there is probable cause to believe that a person has committed a crime and should be indicted for trial. New Hampshire law requires the use of grand juries for certain serious crimes, as specified by state statutes. The proceedings of a grand jury are not open to the public, and the accused and their attorneys do not have the right to appear before the grand jury or to be informed of the proceedings. Witnesses called before the grand jury cannot have their attorneys present during testimony. The number of jurors in a grand jury and the length of their service can vary, but the proceedings are typically transcribed and kept sealed. The specific procedures and requirements for grand juries in New Hampshire are governed by the state's constitution and relevant statutes, which can be found in the state's criminal code and code of criminal procedure.