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The Difference Between a Grand Jury and a Trial Jury – In Plain English

Two Types of Juries: Why the Difference Matters

If you’ve ever watched a courtroom drama or followed a high-profile case in the news, you’ve probably heard the terms “grand jury” and “trial jury” thrown around. Most people assume they’re the same thing — or at least very similar. But in reality, these two types of juries serve completely different purposes in the legal system, and understanding the difference can help you make sense of how criminal procedure actually works in the United States.

Let’s break it all down in plain, simple terms.

What Is a Trial Jury?

A trial jury — also called a “petit jury” — is probably the type you’re most familiar with. This is the group of regular citizens who sit in a courtroom during a trial and decide whether a person is guilty or not guilty of a crime. It’s the jury you see in movies and TV shows, seated in the jury box while attorneys argue their cases.

Key Facts About Trial Juries

Size: A trial jury typically consists of 12 people in serious criminal cases, though some civil cases or less serious criminal matters may use fewer jurors.
Purpose: To listen to the evidence presented at trial and decide the outcome of the case.
Who selects them: Jurors are selected through a process called “voir dire,” where both the prosecution and defense attorneys have a say in who sits on the jury.
Verdict: In most criminal cases, the jury must reach a unanimous decision — meaning all 12 jurors must agree — before a verdict of guilty or not guilty can be delivered.
Open process: Trial proceedings are generally open to the public and the media.

The trial jury is the cornerstone of the American justice system. It reflects a core legal principle — that a person accused of a crime has the right to have their guilt or innocence decided by a group of their peers, not just a single judge.

What Is a Grand Jury?

A grand jury operates very differently. It does not decide whether someone is guilty or innocent. Instead, it decides whether there is enough evidence to formally charge someone with a crime and send the case to trial in the first place.

Think of it this way: a grand jury is like a filter at the front end of the criminal process, while a trial jury comes in at the end.

Key Facts About Grand Juries

Size: A grand jury is larger — typically between 16 and 23 people.
Purpose: To review evidence presented by a prosecutor and decide whether there is “probable cause” to formally charge someone with a crime.
What they decide: If the grand jury agrees there’s enough evidence, they issue what’s called an “indictment.” If they don’t, the case does not move forward to trial.
Secret proceedings: Grand jury hearings are private and confidential. The accused person is typically not present, and neither is the public or the media.
No defense attorneys: During grand jury proceedings, only the prosecutor presents evidence. There is no opposing counsel arguing the other side.
No unanimity required: Unlike a trial jury, a grand jury does not need a unanimous vote. In federal cases, 12 of the 23 jurors must agree to issue an indictment.

Side-by-Side Comparison

Here’s a quick look at how the two types of juries stack up against each other:

Grand Jury: Decides if a case goes to trial. Trial Jury: Decides if a person is guilty.
Grand Jury: 16–23 people. Trial Jury: Usually 12 people.
Grand Jury: Secret and closed to the public. Trial Jury: Open to the public.
Grand Jury: Only the prosecution presents evidence. Trial Jury: Both sides present evidence.
Grand Jury: Issues an indictment or declines to charge. Trial Jury: Returns a verdict of guilty or not guilty.
Grand Jury: Does not require unanimous agreement. Trial Jury: Typically requires a unanimous verdict.

Where Does Each Jury Fit in the Court Process?

To understand how these two juries fit into criminal procedure, it helps to look at the bigger picture of how a criminal case typically moves through the legal system.

A crime is committed and investigated. Law enforcement gathers evidence and builds a case.
The prosecutor reviews the evidence. The prosecutor decides whether to bring the case to a grand jury or file charges directly.
The grand jury reviews the evidence. If the grand jury agrees there’s probable cause, an indictment is issued and the accused is formally charged.
The case goes to trial. This is where the trial jury comes in. Both sides present their arguments and evidence.
The trial jury delivers a verdict. If the jury finds the defendant guilty, the judge then decides the sentence.

It’s important to note that not every criminal case goes through a grand jury. In many states, prosecutors can bypass the grand jury process by filing what’s called a “criminal information” — a formal charge filed directly by the prosecutor. However, under federal law, serious felony cases must go through a grand jury before the accused can be formally charged.

Why Is the Grand Jury Process Controversial?

The grand jury system has received a fair amount of criticism over the years. Because the proceedings are secret and only the prosecution presents evidence, some legal experts argue that grand juries are often too easily influenced by prosecutors. There’s even a famous saying among legal professionals that a skilled prosecutor can “indict a ham sandwich” — meaning it’s not that hard to get a grand jury to agree to charges if only one side of the story is being told.

On the other hand, supporters of the grand jury system argue that it serves as an important check on government power. It forces prosecutors to have at least some evidence before dragging someone through the public and financially draining experience of a full criminal trial.

Your Rights and These Two Types of Juries

Both the grand jury and the trial jury are rooted in constitutional protections. The Fifth Amendment to the U.S. Constitution guarantees the right to a grand jury for serious federal criminal cases. The Sixth Amendment guarantees the right to a speedy and public trial by an impartial jury in criminal prosecutions.

These rights exist to protect ordinary people from being unfairly prosecuted or convicted without due process. Understanding how each type of jury works is a key part of understanding your rights in the legal system.

Common Questions People Ask

Can you be on both a grand jury and a trial jury for the same case?

No. If you served on the grand jury that indicted someone, you would not be eligible to serve on the trial jury for that same case. The roles are separate, and the legal system keeps them that way to ensure fairness.

Does a grand jury indictment mean someone is guilty?

Absolutely not. An indictment simply means that a grand jury found enough evidence to move forward with a trial. The accused person is still presumed innocent until proven guilty at trial.

What happens if a grand jury doesn’t indict?

If a grand jury decides there isn’t enough evidence, they issue what’s known as a “no bill.” This means the case does not move forward — at least not at that time. In some cases, prosecutors may gather more evidence and try again.

The Bottom Line

Both the grand jury and the trial jury play important roles in the American legal system, but they serve very different functions. A grand jury is a private screening process that decides whether enough evidence exists to charge someone with a crime. A trial jury is the public fact-finding body that decides whether the accused is actually guilty.

Understanding these differences gives you a clearer picture of how criminal procedure works from start to finish — and why the legal system has built-in safeguards designed to protect both the accused and the public. Jury law may seem complex, but at its heart, it’s about making sure that decisions with life-changing consequences aren’t made lightly or without proper review.