Cardinals are senior members of the clergy of the Catholic Church. As titular members of the clergy of the Diocese of Rome, they serve as advisors to the pope, who is the bishop of Rome. They are typically ordained bishops and generally hold important roles within the church, such as leading prominent archdioceses or heading dicasteries within the Roman Curia. Cardinals are chosen by the pope and formally created in a consistory, and one of their foremost duties is the election of a new pope – invariably from among their number, although not strictly a requirement – when the Holy See is vacant (sede vacante), following the death or resignation of a pope. Collectively, they constitute the College of Cardinals.
Under current ecclesiastical law, as defined by the apostolic constitution Universi Dominici gregis (1996), only cardinals who have not passed their 80th birthdays on the day on which the Holy See becomes vacant are eligible to take part in a papal conclave to elect a new pope. The same apostolic constitution specifies that no more than 120 cardinals may take part in a conclave, but makes no provision for there being more than 120 eligible cardinal electors, a number that has often been exceeded. Cardinals may be created in pectore (lit. 'in the breast'), in which case the pope does not reveal their identities; they are not entitled to the privileges of a cardinal until their names are published by the pope. The creations of any such cardinals whose names have not been revealed before the pope's death or resignation automatically lapse.