What Is the Difference Between a Jury and a Grand Jury?
A jury and a grand jury are both groups of citizens involved in the U.S. legal system, but they serve different purposes. A trial jury decides whether a defendant is guilty or liable after hearing evidence in court. A grand jury generally decides whether prosecutors have shown enough evidence to bring certain criminal charges. Their proceedings, decision standards, and levels of public access differ, and rules vary by jurisdiction.
The Main Difference Between a Jury and a Grand Jury
The clearest difference is what each group decides. A trial jury—also called a petit jury—decides the outcome of a trial. In a criminal case, it determines whether the prosecution has proved the defendant guilty beyond a reasonable doubt. In a civil case, it may decide whether a party is legally responsible and, in some cases, the amount of damages.
A grand jury usually considers whether there is probable cause to believe a crime was committed and that a particular person committed it. If the required number of grand jurors agrees, the grand jury may return an indictment, a formal criminal charge. It does not decide whether the accused is guilty.
| Feature | Trial jury | Grand jury |
|---|---|---|
| Primary role | Decides a criminal trial or resolves issues in a civil trial | Determines whether evidence supports bringing an indictment in cases where that process is used |
| Key decision | Guilt, liability, or another issue assigned by the court | Whether probable cause supports a formal charge |
| Typical setting | Public courtroom | Usually closed, confidential proceedings |
| Evidence process | Both sides present evidence under courtroom rules | Prosecutors present evidence; the process is generally not an adversarial trial |
| Outcome | Verdict | Indictment, no indictment, or another action permitted by local law |
What a Trial Jury Does
A trial jury listens to evidence presented at trial and applies the law as explained by the judge. Jurors evaluate testimony, exhibits, and other evidence admitted under court rules. They are expected to decide the case based on the evidence and instructions, not on outside research, media coverage, or personal assumptions.
In a criminal trial, the prosecution must prove every element of the charged offense beyond a reasonable doubt. That is a high standard because a conviction can lead to serious consequences, including incarceration. The defendant is presumed innocent, and the defendant does not have to prove innocence. If jurors have a reasonable doubt about guilt, they must return a not-guilty verdict.
In a civil trial, the standard is usually a preponderance of the evidence: whether a claim is more likely true than not. Some civil claims use a higher standard, such as clear and convincing evidence. The judge explains which standard applies to the particular case.
How a trial jury is selected
Potential jurors are commonly summoned from a pool drawn from public records, such as voter-registration or driver’s-license lists, depending on local law. During jury selection, the judge and lawyers question prospective jurors in a process called voir dire. The questions help identify conflicts, bias, or reasons someone may not be able to serve impartially.
Some prospective jurors may be excused for cause, such as a demonstrated inability to be fair. Attorneys may also have a limited number of peremptory challenges, subject to legal restrictions. The final group is sworn in to hear the case. A trial may also include alternate jurors who can replace a juror who becomes unable to serve.
How a trial jury reaches a verdict
After the evidence and closing arguments, the judge instructs jurors on the relevant law. Jurors then deliberate privately and attempt to reach a verdict. In federal criminal cases, a guilty verdict must be unanimous. The U.S. Supreme Court has also held that state criminal convictions for serious offenses require unanimous jury verdicts.
In federal civil cases, the verdict generally must be unanimous unless the parties agree otherwise. State rules and the type of case can affect civil jury requirements. If jurors cannot reach the required agreement, the judge may declare a mistrial, and the case may be retried or resolved in another way.
What a Grand Jury Does
A grand jury is a group of citizens convened to review potential criminal conduct. Federal prosecutors may use one to investigate suspected federal crimes and seek an indictment. State systems differ: some require grand-jury indictments for particular charges, while others rely more heavily on prosecutors filing charges directly or on preliminary hearings before a judge.
The grand jury’s central question is generally whether there is probable cause to believe that an offense occurred and that the person named committed it. Probable cause is a lower standard than proof beyond a reasonable doubt. An indictment therefore authorizes a case to proceed; it is not a finding of guilt and does not establish that the accused committed the crime.
Grand juries can also investigate. Prosecutors may present documents and witness testimony, and the grand jury may issue subpoenas under applicable rules. A subpoena can require a person to testify or produce records. The scope and limits of these powers depend on the jurisdiction, the matter under investigation, and constitutional protections.
How federal grand-jury proceedings work
Under the Federal Rules of Criminal Procedure, a federal grand jury generally has 16 to 23 members. At least 12 jurors must agree to return an indictment. Federal grand-jury proceedings are ordinarily conducted in secret. The secrecy rules are intended to protect the investigation, encourage candid testimony, and reduce unnecessary harm to people who are investigated but not charged.
The prosecutor presents the matter and advises the grand jury about applicable law. The accused and defense lawyer generally are not present in the grand-jury room during witness testimony, and there is usually no judge presiding over the proceeding. A witness may have a lawyer available outside the room, subject to the rules that apply. These features distinguish the process from a trial, where the defense can challenge the prosecution’s evidence in open court.
Federal grand-jury proceedings are governed by Rule 6 of the Federal Rules of Criminal Procedure. State procedures can differ in membership, secrecy, voting rules, and the grand jury’s authority. The federal model should not be assumed to apply identically in every state.
How the Standards of Proof Differ
The different standards reflect the different jobs of the two groups. A grand jury’s probable-cause decision is a threshold determination about whether a criminal case may move forward through an indictment. A trial jury’s decision comes after the parties have had an opportunity to present and challenge evidence, and it resolves whether the prosecution has met the much higher burden of proof beyond a reasonable doubt.
That distinction is important in practice. An indictment can be issued even though a later trial jury acquits the defendant. The two decisions are not inconsistent: the grand jury may have found enough evidence to justify a charge, while the trial jury may later conclude that the evidence does not prove guilt beyond a reasonable doubt.
Public Access, Secrecy, and the Defendant’s Role
Trials are generally open to the public, subject to limited exceptions ordered by a court. Public proceedings allow people to observe how evidence is presented and how a case is decided. The defendant has important rights in a criminal trial, including the right to be represented by counsel and, in many circumstances, the right to confront witnesses.
Grand-jury proceedings are generally confidential and not open to the public. The defendant usually does not present a defense or cross-examine witnesses during the proceeding. Confidentiality does not mean grand-jury evidence is automatically hidden forever: information may become public through later court proceedings, and disclosure may be allowed under specific legal rules. The exact rules depend on whether the investigation is federal or state and on the circumstances.
What Happens After a Grand Jury Acts?
If a federal grand jury returns an indictment, the case generally proceeds to court. The defendant appears, receives notice of the charges, and can challenge the case through the procedures available under criminal law. The prosecution still has to prove guilt beyond a reasonable doubt at trial unless the case is resolved by a guilty plea or another lawful disposition.
If a grand jury does not return an indictment, the prosecutor may be unable to proceed on that proposed indictment at that time. The result does not necessarily prevent every future charge. Depending on the law and facts, prosecutors may continue investigating, present additional evidence, pursue different charges, or use another procedure. A grand jury’s decision is not the same as a trial acquittal.
Some criminal cases begin through a complaint or information rather than a grand-jury indictment. In federal felony cases, the Fifth Amendment generally requires a grand-jury indictment unless the defendant waives that right, with exceptions such as certain cases in the armed forces or during public danger. State constitutional and statutory rules determine when a state grand jury is required.
Common Misconceptions About Juries and Grand Juries
- “An indictment means the defendant is guilty.” It does not. An indictment is a formal accusation, not a verdict.
- “The grand jury hears both sides like a trial jury.” Usually it does not. The prosecutor typically presents evidence, and the defense generally does not participate in the same way it does at trial.
- “A grand jury decides the sentence.” It does not. Sentencing occurs later if there is a conviction, and the judge generally imposes the sentence under applicable law.
- “Every criminal case goes before a grand jury.” That is not true. Requirements vary by jurisdiction and charge, and many cases proceed through other charging procedures.
- “A trial jury always has 12 members.” Not necessarily. Jury size can depend on the court, case type, and applicable law. Federal criminal juries generally have 12 members unless the rules permit a different arrangement.
Why the Difference Matters
Knowing the difference between a jury and a grand jury helps clarify what a headline or court document means. “Indicted” means formal charges have been brought through the applicable process; it does not mean the defendant has been convicted. “Acquitted” means a trial jury found the prosecution did not prove guilt to the required standard. Those terms describe distinct stages and decisions.
The distinction also explains why a grand jury’s work is generally confidential and why a trial is structured to let both sides test evidence. One process assesses whether charges are supported enough to proceed; the other determines the outcome after a case is presented in court. Because federal and state rules differ, a specific case may require checking the law and procedures of the court handling it.
Sources and Further Reading
- U.S. Courts: Juries — overview of federal jury service and jury roles.
- Federal Rule of Criminal Procedure 6 — federal grand-jury size, proceedings, and secrecy.
- Federal Rule of Criminal Procedure 23 — jury trial and jury size in federal criminal cases.
- Ramos v. Louisiana — U.S. Supreme Court decision on unanimity in state criminal jury verdicts for serious offenses.
- Constitution Annotated: Fifth Amendment — grand-jury indictment protections and exceptions.