Diocesan administrators in canon law 
The college of consultors elects an administrator within eight days after the see is known to be vacant. The college must elect as administrator a priest or bishop at least 35 years old. If the college of consultors fails to elect a priest of the required minimum age within the time allotted, the choice of diocesan administrator passes to the metropolitan archbishop or, if the metropolitan see is vacant, to the senior by appointment of the suffragan bishops of the ecclesiastical province.
If a diocese has a coadjutor bishop, the coadjutor succeeds immediately to the episcopal see upon the previous bishop's death or resignation, and there is no vacancy of the see. The see also does not become vacant if the Pope appoints an apostolic administrator.
Before the election of the diocesan 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 diocesan administrator has greater powers, essentially those of a bishop except for matters excepted by the nature of the matter or expressly by law. 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). The diocesan administrator remains in charge until a new bishop takes possession of the see or until he presents his resignation to the college of consultors.
An episcopal conference can transfer the functions of the consultors to the cathedral chapter. In those countries in which the episcopal conference has transferred the functions, the cathedral chapter, and not the consultors, elect the diocesan administrator. Capitular election was the default rule before the adoption of the 1983 Code of Canon Law; this old default rule is reflected in the term for the equivalent of a diocesan administrator in the 1917 code: vicar capitular.
Administrators of prince-bishoprics 
Since the Investiture Controversy in 11th and 12th the cathedral chapters used to elect the Catholic bishops in the Holy Roman Empire. Prince-bishoprics were elective monarchies of imperial immediacy within the Empire, with the monarch being the respective bishop usually elected by the chapter and confirmed by the Holy See, or exceptionally only appointed by the Holy See. Papally confirmed bishops were then invested by the emperor with the princely regalia, thus the title prince-bishop. However, sometimes the respective incumbent of the see never gained a papal confirmation, but was still invested the princely power. Also the opposite occurred with a papally confirmed bishop, never invested as prince.
Candidates elected, who lacked canon-law prerequisites and/or papal confirmation, would officially only hold the title diocesean administrator (but nevertheless colloquially be referred to as prince-bishop). This was the case with Catholic candidates, who were elected for an episcopal see with its revenues as a mere appanage and with all Protestant candidates, who all lacked either the necessary vocational training or the papal confirmation.
With many capitulars converting to Lutheranism or Calvinism during the Reformation, the majorities in many chapters consisted of Protestant capitulars. So they then also elected Protestants as bishops, whom usually were denied papal confirmation. However, in the early years of Reformation, with the schism not yet fully implemented, it was not always obvious, who tended to Protestantism, so that some candidates only turned out to be Protestants after they had been papally confirmed as bishop and imperially invested as prince. Later, when Protestants were usually denied papal confirmation, the emperors nevertheless invested the unconfirmed candidates as princes - by a so-called liege indult (German: Lehnsindult) - due to political coalitions and conflicts within the empire, in order to gain candidates as imperial partisans.
Many Protestant candidates, elected by the capitulars, neither achieved papal confirmation nor a liege indult, but nevertheless, as a matter of fact held de facto princely power. This was because the emperor would have to use force to bar the candidates from ruling, with the emperors lacking the respective power or pursuing other goals. A similar situation was in a number of imperially immediate abbeys with their prince-abbots and princess-abbesses.
As administrators the incumbents of the sees had comparable power like any other monarch of an imperially immediate territory within the Empire, just being elected instead of having succeeded by way of inheritance. However, one common restriction was that administered prince-bishoprics were denied to emit their deputees to the diets of the Empire or of the imperial circles (German: Reichstag, or Kreistag, respectively). This restriction was abandoned by the Peace of Westphalia in 1648, when the emperor accepted Protestant administrators as fully empowered rulers. However, the Peace also secularised many of the prior Protestant prince-bishoprics and transformed them into hereditary monarchies.
Prince-bishoprics ruled by Protestant administrators 
Prince-bishoprics, which were ruled by Protestants, were the following:
- Prince-Bishopric of Brandenburg, Lutheran bishops and administrators since 1539, secularised and merged into the Electorate of Brandenburg in 1571.
- Prince-Archbishopric of Bremen, Lutheran administrators since 1567, secularised as hereditary Duchy of Bremen in 1648
- Prince-Bishopric of Cammin, Lutheran bishops and administrators since 1544, secularised and merged into the Duchy of Pomerania in 1650
- Prince-Bishopric of Halberstadt, Lutheran administrators 1566-1628, after the rule of the last, however, Catholic administrator, secularised as Principality of Halberstadt in 1648
- Prince-Bishopric of Havelberg, Lutheran bishops and administrators since 1558, secularised and merged into the Electorate of Brandenburg in 1598.
- Prince-Bishopric of Lebus, Lutheran bishop and administrators since 1555, secularised and merged into the Electorate of Brandenburg in 1598.
- Prince-Bishopric of Lübeck, Lutheran bishops and administrators in 1535 and from 1555 on, secularised as Principality of Lübeck in 1803
- Prince-Archbishopric of Magdeburg, Lutheran administrators between 1566 and 1631 and again since 1638, secularised as hereditary Duchy of Magdeburg in 1680
- Prince-Bishopric of Merseburg, Lutheran administrators since 1544, secularised and merged into the Electorate of Saxony in 1565
- Prince-Bishopric of Minden, Lutheran administrators between 1554 and 1631, after the rule of the last, however, Catholic prince-bishop, secularised as Principality of Minden in 1648
- Prince-Bishopric of Naumburg, Lutheran bishop and administrators between 1542 and 1547 and from 1562 on, secularised and merged into the Electorate of Saxony in 1615
- Prince-Bishopric of Osnabrück, Lutheran bishops and administrators between 1574 and 1623, and Lutheran administrators and Catholic bishops in alternate succession since 1634, secularised and merged into the Electorate of Brunswick and Lunenburg in 1803
- Prince-Bishopric of Ratzeburg, Lutheran administrators since 1554, secularised as the Principality of Ratzeburg in 1648
- Prince-Bishopric of Schwerin, Lutheran administrators since 1533, secularised as the Principality of Schwerin in 1648
- Prince-Bishopric of Verden, Lutheran bishop and administrators between 1574 and 1630, and, after the rule of the last, however, Catholic prince-bishop, from 1631 on, secularised as Principality of Verden in 1648
- Code of Canon Law, canon 421 §1.
- Code of Canon Law, canon 425 §1. The word used in the canon (sacerdos) is not limited to a priest and applies also to a bishop.
- Code of Canon Law, canons 421 §2 and 425 §3.
- Code of Canon Law, canons 426-427
- Code of Canon Law, canons 430
- Codex Iuris Canonici Canon 502 § 3.
- See Codex Iuris Canonici Canon 421 § 1 (noting that the consultors elect the administrator, "without prejudice to the provisions of can. 502 §3").
- Codex Iuris Canonici Canons 431–432 (1917).