In most criminal cases the charge is first considered by a grand jury with 12 to 23 members. It hears witnesses against the accused, and if 12 jurors believe that there is sufficient evidence to prosecute, an indictment or the like is presented. The jury sitting at the trial proper is called a petit (or petty) jury from its smaller size (usually 12 members).
The selection of a trial jury is essentially alike in civil and in criminal cases. The venire, a panel of prospective jurors living in the district where the trial is to be held, is summoned for examination. Counsel for the parties may first challenge the array, that is, object that the venire as a whole was improperly chosen or is for some reason unfit. The challenges to the poll (the members of the venire taken individually) that follow are designed to secure as jurors unbiased persons without special knowledge of the matters in issue. Included are challenges for principal cause, i.e., some grounds such as relationship to a party that requires dismissal of a member of the venire; challenges to the favor, i.e., suspicion of unfitness on which the judge rules; and a limited number of peremptory challenges. Once selected, the jury (usually with several alternates) takes an oath to act fairly and without preconceptions. At the close of the evidence and after the summations of counsel the judge instructs the jury concerning the verdict. Outside the English-speaking countries there is generally less recourse to the jury and less care in the selection of jurors.
The value of juries in civil trials is disputed. Opponents of juries argue that they are ineffective, irrational, and cause delay; proponents argue that juries bring community standards to bear, can modify the effects of harsh laws, and are a protection against incompetent judges. Critics also have argued that juries are responsible for huge, arbitrary punitive damage awards in malpractice, product liability and similar cases, but an extensive 2001 study of actual cases found that juries and judges tend award punitive damages as often and to the same degree.