Pope Francis will officiate on Sunday at the beatification of John Paul I, who was head of the Catholic Church for just 33 days before he died in strange circumstances.
Mass in St. Peter's Square is expected to be attended by thousands of people.
Beatification is the last step before a person can be canonized.
John Paul I was elected Pope on August 26, 1978, when he was 65 years old.
He died just 33 days later, on September 28, becoming the shortest-serving head in the recent history of the Catholic Church.
The cause of his death was given as a heart attack.
The death of Pope John Paul I has caused much speculation.
Some believe it was suicide, as he seemed unwilling to take office.
It was also speculated that John Paul I was killed by his opponents, that is opponents of the reforms of the Catholic Church, which he supposedly advocated, especially those related to the Vatican Bank.
These conspiracy theories were dismissed by many, and biographer Christophe Henning said that the cause of these rumors could simply be the sudden nature of the Pope's death, combined with the fact that at the time the Vatican did not have adequate communication with the public.
But an autopsy to determine the cause of death has not been performed and the Vatican has released inconsistent information about what happened.
In October 2021, the Vatican announced that it recognized the miracle attributed to John Paul I, which allowed him to be beatified.
The miracle was the alleged sudden recovery of a seriously ill 11-year-old girl in Buenos Aires in 2011 after a local priest prayed to the late pope.
According to the rules of the Catholic Church, in most cases, a second miracle must be recognized before someone can be declared a saint.
John Paul is said to have stood by the Church's opposition to abortion and contraception, but he also tried to reform the way the Catholic Church was governed.
Among the most recent popes, John XXIII (1958-63), Paul VI (1963-78) and John Paul II (1978-2005) were canonized.
Pope Francis' predecessor, Benedict XVI, resigned in 2013 and still lives in the Vatican.