California Grand Jury's are unique because of their civil oversight function. They were established to protect citizens and society and keep a watchful eye on certain aspects of government. In 1791 Grand Juries became part of the United States Constitution, the Fifth Amendment, and part of the California Constitution in 1879.

In California, there are two types of juries, the petit jury and the grand jury.

• The petit jury is the well-known trial jury, usually composed of 12 members that are chosen from county citizens that are summoned to appear for jury services. It is this jury that sits as chosen and decides the guilt or innocence of the individual on trial.
  
  
• The grand juries tend to be larger and serve a different purpose. Under California law the Ventura County Grand Jury is composed of 19 members that are selected to serve for one year. The Grand Jury function is to act as a civil oversight of county and city government, special districts, governing boards, personnel commissions, school districts, or humane officers. It is their responsibility to insure that government is serving the best interests of Ventura County's citizens.

When necessary the District Attorney may also call for a special Criminal Grand Jury to consider a filed indictment. That jury is chosen the same way as a petit jury and serves a limited time. Their function is to determine if there is probable cause to consider that the person being charged committed a crime and there is sufficient evidence to warrant a trial.

California grand juries hold inquiries and perform investigations. The grand jury does not decide guilt or innocence. Its function is inquisitorial and accusatorial, unlike that of the petit jury, which tries cases. The Grand Jury enjoys greater independence than the petit jury, and its investigations are relatively free from supervision. Although the jury works with the County Council for legal guidance, it is not under their control.

Its power over witnesses resembles that of a trial court. Witnesses must appear and usually must testify. Refusal may constitute contempt. Examination of witnesses is at the jury's discretion. The proceedings are secret and informal.