Gregory XV becomes Pope, the last Pope elected by acclamation.

Pope Gregory XV, born Alessandro Ludovisi, was the head of the Catholic Church and ruler of the Papal States from 9 February 1621 until his death in 1623. He is notable for founding the Congregation for the Propagation of the Faith, an organization tasked with overseeing the spread of Catholicism and missionary work. Gregory XV was also responsible for the canonization of Saints Ignatius of Loyola, Francis Xavier, Teresa of Ávila, and Philip Neri, which solidified his commitment to the Counter-Reformation.

The pope is the bishop of Rome and the visible head of the worldwide Catholic Church. He is also known as the supreme pontiff, Roman pontiff, or sovereign pontiff. From the 8th century until 1870, the pope was the sovereign or head of state of the Papal States, and since 1929 of the much smaller Vatican City state. From a Catholic viewpoint, the primacy of the bishop of Rome is largely derived from his role as the apostolic successor to Saint Peter, to whom primacy was conferred by Jesus, who gave Peter the Keys of Heaven and the powers of "binding and loosing", naming him as the "rock" upon which the Church would be built. The current pope is Leo XIV, who was elected on 8 May 2025 on the second day of the 2025 papal conclave.

A conclave is a gathering of the College of Cardinals convened to appoint the pope of the Catholic Church. Catholics consider the pope to be the apostolic successor of Saint Peter and the earthly head of the Catholic Church.

Acclamation was formerly one of the methods of papal election.