Sede vacante (lit. 'with the chair [being] vacant' in Latin)^{[lower-alpha 1]} is a term for the state of a/an (arch)diocese while without a/an (arch)bishop. In the canon law of the Catholic Church, the term is used to refer to the vacancy of the (arch)bishop's or Pope's authority upon his death or resignation.

Early in church history, the archpriest, archdeacon, and "primicerius of the notaries" in the papal court made a regency council which governed the sede vacante period.^[2]

It was the obligation of the Camerarius (papal chamberlain), the head of the Camera Apostolica, to formally establish the death of the pope. Gradually, this evolved in the theory that the Camerarius, as the chief of the curia, should conduct normal business even after the death of the pope, and also conduct the burial and the preparation for the new election. This process was evident with Camerarius Boso Breakspeare.^[3] During the long sede vacante of 1268 to 1271, the importance of the Camerarius was so clear that the Cardinals were ready to elect a new one if he died.^[3]

After the death or resignation of a pope, the Holy See enters a period of sede vacante. In this case the particular church is the Diocese of Rome and the "vacant seat" is the cathedra of Saint John Lateran, the cathedral church of the Bishop of Rome. During this period, the Holy See is administered by a regency of the College of Cardinals.

According to Universi Dominici gregis, the government of the Holy See and the administration of the Catholic Church during sede vacante falls to the College of Cardinals, but in a very limited capacity. At the same time, all the heads of the departments of the Roman Curia "cease to exercise" their offices. The exceptions are the Cardinal Camerlengo, who is charged with managing the property of the Holy See, and the Major Penitentiary, who continues to exercise his normal role. If either has to do something which normally requires the assent of the Pope, he has to submit it to the College of Cardinals. Papal legates continue to exercise their diplomatic roles overseas, and both the Vicar General of Rome and the Vicar General for the Vatican City State continue to exercise their pastoral role during this period. The postal administration of the Vatican City State prepares and issues special postage stamps for use during this particular period, known as "sede vacante stamps".

The coat of arms of the Holy See also changes during this period. The papal tiara over the keys is replaced with the umbraculum, or ombrellino in Italian. This symbolizes both the lack of a Pope and the governance of the Camerlengo over the temporalities of the Holy See. As further indication, the Camerlengo ornaments his arms with this symbol during this period, which he subsequently removes once a pope is elected. Previously during this period the arms of the Camerlengo appeared on commemorative Vatican lira coinage. It now makes its appearance on Vatican euro coins, which are legal tender in all Eurozone states.

The interregnum is usually highlighted by the funeral Mass of the deceased pope, the general congregations of the College of Cardinals for determining the particulars of the election, and finally culminates in the papal conclave to elect a successor. Once a new pope has been elected (and ordained bishop if necessary) the sede vacante period officially ends, even before the papal inauguration.

Cardinals present in Rome are required to wait at least fifteen days after the start of the vacancy before they hold the conclave to elect the new Pope. After twenty days have elapsed, they must hold the conclave, even if some cardinals are missing. The period from the death of the Pope to the start of the conclave was often shorter but, after William Henry Cardinal O'Connell had arrived just too late for two conclaves in a row, Pius XI extended the time limit. With the next conclave in 1939, cardinals began to travel by air. Days before his resignation in February 2013, Benedict XVI amended the rules to allow the cardinals to begin the conclave sooner, if all voting cardinals are present.^[4] Historically, sede vacante periods have often been quite lengthy, lasting many months, or even years, due to lengthy deadlocked conclaves.

The most recent period of sede vacante of the Holy See began on 28 February 2013, after the resignation of Benedict XVI,^[5] and ended on 13 March 2013 with the election of Pope Francis, a period of 13 days.

The longest period without a Pope in the last 250 years was the approximately half year from the death in prison of Pius VI in 1799 and the election of Pius VII in Venice in 1800.

The term sede vacante can be applied to Catholic dioceses, archdioceses, and eparchies outside of Rome. In such cases, this means that the particular diocesan bishop or archbishop has either died, resigned, been transferred to a different diocese or archdiocese, or lost his office and a successor has not yet been installed. If there is a coadjutor bishop for the (arch)diocese, then this period does not take place, as the coadjutor bishop or archbishop immediately succeeds to the episcopal see.

Within eight days after the episcopal see is known to be vacant, the college of consultors (or the cathedral chapter in some countries)^[7] is obliged to elect a diocesan or archdiocesan administrator.^[8] The administrator they choose must be a priest or bishop who is at least 35 years old.^[9]

If the college of consultors fails to elect a qualifying person within the time allotted, the choice of an administrator passes to the metropolitan archbishop or, if the metropolitan see is vacant, to the senior-most by appointment of the suffragan bishops. The pope can also decide to name an administrator himself to a diocese or archdiocese instead of waiting for the college of consultors of a particular (arch)diocese to appoint a/an (arch)diocesan administrator where it is then called as apostolic administrator. Usually, the emeritus (arch)bishop will be appointed in such a case. If the appointed apostolic administrator is a diocesan bishop or archbishop of a diocese or archdiocese, then he governs two (arch)dioceses which are his own and the vacant one, with the latter being temporarily while a successor of a vacant (arch)diocese is not yet installed or assumed office.^[10]

Before the election of the administrator of a vacant see, the governance of the see is entrusted, with the powers of a vicar general, to the auxiliary bishop, if there is one, or to the senior among them, if there are several, otherwise to the college of consultors as a whole. The administrator has greater powers, essentially those of a bishop or archbishop except for matters excepted by the nature of the matter or expressly by law.^[11] Canon law subjects his activity to various legal restrictions and to special supervision by the college of consultors (as for example canons 272 and 485).

Vicars general and episcopal vicars lose their powers sede vacante if they are not bishops or archbishops;^[12] the vicars that are themselves having both positions retain the powers they had before the see fell vacant, which they are to exercise under the authority of the administrator.^[13]

A coat of arms of the last (arch)bishop of a/an (arch)diocese may also be used during sede vacante period as placeholder to indicate and establish continuity while awaiting for the installation of a successor. Once a successor is installed or assumed office which ends the sede vacante period, the coat of arms of a new (arch)bishop will then be used by the (arch)diocese and discontinuing the usage of the predecessor's arms.

The term has been adopted in sedevacantism, an extreme^[14][15][16] strand of the Catholic traditionalist movement. Sedevacantists believe that all popes since the Second Vatican Council have been heretics, and that therefore the see of Rome is vacant.

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