A grand jury is a type of common law jury; responsible for investigating alleged crimes, examining evidence, and issuing indictments. A grand jury is chosen from the same pool of people that provide trial jurors. Consequently grand juries tend to be composed of the same kinds of people who serve on regular, trial juries (like the juries in the O.J. Simpson civil and criminal cases).

A grand jury can compel witnesses to testify. During the proceeding, the defendant and his or her counsel are generally not present. The grand jury's decision is either "true bill" or "no true bill." Where they exist, grand juries are part of the system of checks and balances that prevents prosecutors from harassing citizens with groundless prosecution. Before a defendant is ever forced to defend himself, the grand jury must find a "true bill" and issue an indictment.

Most jurisdictions have abolished grand juries, replacing them with the preliminary hearing at which a judge hears evidence concerning the alleged offenses and makes a decision on whether the prosecution can proceed. However, grand juries are still used in a number of US jurisdictions.

The United States

Charges involving "capital or infamous crimes" under federal jurisdiction must be presented to a grand jury, under the Fifth Amendment to the United States Constitution. This has been interpreted to permit bypass of the grand jury for misdemeanor offenses, which can be charged by prosecutor's information.

Unlike many other provisions of the Bill of Rights, the Supreme Court has ruled that this requirement does not pertain to the state courts, and states are free to abolish grand juries.

Criticism of the Grand Jury

Some argue that the grand jury is unjust as the defendant is not represented by counsel and/or does not have the right to call witnesses.

In practice, a grand jury rarely acts in a manner contrary to the wishes of the prosecutor and as such many jurisdictions in the United States have replaced the formality of a grand jury with a procedure in which the prosecutor can issue charges by filing an information (also known as an accusation) which is followed by a preliminary hearing before a judge at which both the defendant and his or her counsel are present.

In some jurisdictions, defendants have the option of testifying before the grand jury. Police officers who are accused of crimes in the course of their jobs, such as after the shooting of a suspect, sometimes take the opportunity to give the grand jury their side of the story. Grand juries in such situations frequently refuse to indict.

In all US jurisdictions retaining the grand jury, the defendant has the privilege under the Fifth Amendment not to give self-incriminating testimony. However, the prosecutor can call the defendant to testify and require the defendant to assert the privilege on a question-by-question basis, which is prohibited in jury trials unless the defendant has voluntarily testified on his own behalf. Other evidentiary rules applicable to trials (such as the hearsay rule) are generally not applicable to grand jury proceedings.