A Titular See is a diocese that is no longer in existence. In Asia Minor and North Africa, many dioceses became defunct over them when they became schismatic, or when they were swept by other religions, or when they disappeared simply because the importance of the cities declined. The Apostolic See can also suppress a diocese when the number of Catholics in the diocese has declined sharply.

The nomination of Titular Archbishops and Bishops is reserved to the Holy See. Their former title "in partibus infidelium" was changed in 1882 to that of "Titular Bishops". They have no jurisdiction over their titular dioceses, but enjoy, with few exceptions, the privileges and honours of residential Bishops.

Bishops who are assigned to a Titular Metropolitan See or Titular Archiepiscopal See are Titular Archbishops. However, Bishops who are assigned to a Titular Episcopal See may also be Titular Archbishops.