The right to a jury trial is guaranteed by the Sixth Amendment of the U.S. Constitution. This guarantee is applicable to the states and applies only to criminal cases. Few cases utilize a trial jury. The public perceives jury service as either an honor or a disruption. The ability to serve on a jury is limited by age, U.S. citizenship, felony conviction, and professional exemptions.
A jury is comprised of the defendant's peers, though this does not mean that the jury will resemble the defendant. Potential jurors are assembled using master lists, which are compiled from a variety of sources. Potential jurors are contacted by court clerks or jury commissioners. The frequency with which people can be called for jury service varies by state.
A twelve-member jury is selected from a group of thirty-six to forty-eight potential jurors. During selection, potential jurors are questioned in a process called voir dire. The attorneys for both sides are able to exclude potential jurors through challenges for cause or peremptory challenges. Challenges for cause are used when a person has a prejudice or prejudgment regarding the case. Peremptory challenges may be exercised by each attorney in limited number, and no reason needs to be given for the challenge. However, peremptory challenges cannot be exercised in a discriminatory way. Each attorney's goal is to choose a jury that is most advantageous to their side, which usually results in the selection of a neutral jury.
A juror's duty is to listen to the evidence and decide what the truth is. The judge gives instructions to the jury, and the jury begins deliberations by selecting a foreperson and determining a verdict. Juries are traditionally composed of twelve people, though smaller juries can be used in some instances. Smaller juries save time and money, but may not be truly representative. Traditionally, jury verdicts must be unanimous. This is always necessary in death penalty cases, though there are some instances where a unanimous verdict may not be required. If there is a hung jury, which is a jury that cannot reach a unanimous verdict, the judge may either dismiss the charges or retry the case.
Lay witnesses, or eyewitnesses, are individuals who have personal knowledge of facts. Lay witnesses can testify about anything that they have perceived through their physical senses. Expert witnesses testify regarding their professional opinions on issues. Their expertise must be established, and they are generally paid for their testimony. Attorneys are allowed to take depositions of expert witnesses prior to trial.
Bailiffs are responsible for providing courtroom security and other functions. Court scheduling is handled by court clerks and administrators. Roscoe Pound's four principles of court reform are court unification, judicial superintendents, administrative personnel, and policy research. Administrative personnel became a significant issue as it emerged as a profession in the 1970s. Court administrators have responsibility for budgeting, personnel administration, jury management, and case scheduling. Court reporters are responsible for maintaining a verbatim transcript of court proceedings, and interpreters provide assistance in other languages.