A coadjutor bishop is a bishop in the Catholic, Anglican, and Eastern Orthodox churches whose main role is to assist the diocesan bishop in the administration of the diocese. The coadjutor is a bishop himself, although he is also appointed as vicar general. The coadjutor bishop is, however, given authority beyond that ordinarily given to the vicar general, making him co-head of the diocese in all but ceremonial precedence. In modern times, the coadjutor automatically succeeds the diocesan bishop upon the latter's retirement, removal, or death.
In the Roman Catholic Church, a coadjutor bishop is an immediate collaborator of the diocesan bishop, similar to an auxiliary bishop. However, unlike auxiliary bishops, coadjutors are given the right of succession to the episcopal see. When the diocesan bishop dies, retires, resigns, or is reassigned, the coadjutor automatically becomes the next bishop of the local Church. Until then, the diocesan bishop appoints the coadjutor to act as vicar general. He needs to be a bishop, and, in a now-discontinued practice, held a titular see until his succession. In modern church practice, the appointment of a coadjutor is usually done in cases where a diocesan bishop feels that he will not be able to continue in his position for health reasons or impending retirement. In such cases, the Pope may assign a coadjutor in order to give him time to become familiar with the diocese that he will eventually take over. For example, Bishop Dennis Marion Schnurr of the Diocese of Duluth, Minnesota, was named Coadjutor Archbishop of the Archdiocese of Cincinnati, Ohio, in 2008 to succeed aging Archbishop Daniel Edward Pilarczyk. At times, the appointment of a coadjutor is used to discreetly remove a diocesan bishop who has become involved in scandal or other problems. An example of this occurred in the Archdiocese of Dubuque in the 1940s, when Archbishop Francis Beckman involved the archdiocese in what turned out to be a dubious mining scheme. When the scheme fell apart and resulted in serious financial problems for Beckman and the archdiocese, Bishop Henry Rohlman, of Davenport, Iowa, was appointed Coadjutor Archbishop of Dubuque. While Beckman was allowed to retain the office of Archbishop, it was made clear to him by the Holy See that the actual power rested with Rohlman. Prior to the reform of the Code of Canon Law in 1983, a distinction was made between coadjutor bishops cum jure succesionis and those without. Some coadjutors were appointed with the right of succession, and others were without such a right, usually as archbishops in particularly large dioceses who also held other important posts and to honor certain auxiliary bishops. For an example of a coadjutor without right of succession, see John J. Maguire, coadjutor archbishop of New York. Now, every coadjutor who is appointed has the concomitant right of succession. An Apostolic Vicar may also have a coadjutor, who, like him, will be a titular bishop.
In some provinces of the Anglican Communion, a bishop coadjutor is a bishop elected or appointed to follow the current diocesan bishop upon the incumbent's death or retirement. For example, in the Episcopal Church in the United States of America, when a diocesan bishop announces a retirement, a special diocesan convention is held to elect a coadjutor. Usually, the coadjutor serves with the incumbent for a short time before the latter's retirement, when the coadjutor becomes the diocesan bishop. Bishops coadjutor are also appointed in the Reformed Episcopal Church. The role of "assistant bishop" in the Church of England is fulfilled by a suffragan. There have been bishops coadjutor in the Anglican Church of Australia without the right of succession to the diocesan see.