Aeterni Patris Filius

Jus novum (c. 1140-1563) Jus novissimum (c. 1563-1918) Jus codicis (1918-present) Other Sacraments Sacramentals Sacred places Sacred times Supra-diocesan/eparchal structures Particular churches Juridic persons Philosophy, theology, and fundamental theory of Catholic canon law Clerics Office Juridic and physical persons Associations of the faithful Pars dynamica (trial procedure) Canonization Election of the Roman Pontiff Academic degrees Journals and Professional Societies Faculties of canon law Canonists Institute of consecrated life Society of apostolic life Aeterni Patris Filius (English: Son of the Eternal Father), also called Aeterni Patris, was a bull issued by Pope Gregory XV on 15 November 1621 that regulated papal conclaves.

Together with the bull Decet Romanum pontificem of 1622, it formed the canonical basis for papal elections until the 20th century.

It established general rules for the conclave process, while the later bull Decet Romanum pontificem addressed the ceremonial aspects of papal elections.

[1] Gregory instituted the rule that to win election by scrutiny, a candidate must secure two-thirds of the votes of the electors in the conclave in a secret ballot.

This reform decreased the power of the leaders of individual factions in the conclave and angered many Catholic monarchs.