In the Roman Catholic governance the vacant seat (in Latin, sede vacante) is the interregnum between a Pope's death or resignation and the election of his successor. (More broadly, the term is used for a vacancy in any diocese; thus if a person is named to administer a vacant see by the Pope, he is Apostolic Administrator sede vacante of that see. Such an appointment would pre-empt local election of the administrator).

According to Universi Dominici Gregis, during the sede vacante the government of the Holy See (and therefore of the Roman Catholic Church) falls to the College of Cardinals, but in a very limited capacity.

Most of the members of the Roman Curia lose their offices when a sede vacante occurs. The exceptions are the Cardinal Camerlengo and the Major Penitentiary, who continue to exercise their normal roles. If they have to do something which normally requires the assent of the Pope, though, they have to submit it to the College of Cardinals.

Cardinals present in Rome are required to wait at least fifteen days after the start of the sede vacante for the rest of the college before they can hold the conclave to elect the new Pope. However, after twenty days have elapsed, they must hold the conclave even if cardinals are missing.

See also sedevacantism, the belief among some Traditional Catholics that the sitting Pope is not a true Pope due to heresy.