Time stops at the Vatican between the death of a Pope and the ascension to the throne of a successor.
With the death of a Pope, much of the central administration of the Roman Catholic Church grinds to a halt while a cardinal known as the camerlengo, or chamberlain, becomes a kind of interim chief, albeit with very limited powers.
The camerlengo officially ascertains the Pope's death and seals his private apartments. He is also responsible for preparing both for the Pontiff's funeral and for the conclave to elect a successor. According to pre-written Church rules, the Pontiff's mourning rites will last 9 days and his body will be laid to rest in the crypt underneath St Peter's Basilica.
His funeral was expected to be in mid-week - Italian media said on Wednesday - and many world leaders were expected to attend, including President George W Bush.
The conclave to elect a new Pope will start in 15 to 20 days, with 117 cardinals from around the globe gathering in the Vatican's Sistine Chapel to choose a successor. Until a conclave has chosen a new Pope, the governing of the Church is entrusted to the Sacred College of Cardinals, but only for what Church rules call "ordinary business and matters which cannot be postponed".
The cardinals, who meet periodically, have no jurisdiction in matters which pertained to the late Pope and cannot correct or modify Church laws or teachings issued by him.
A General Congregation - composed of all cardinals as they arrive in Rome - makes decisions on important affairs, while a Particular Congregation - made up of the camerlengo and three elected cardinal assistants - decides on routine matters.
Among the Particular Congregation's first decisions are when the Pope's body is to be taken into St Peter's Basilica for viewing by the faithful and to fix the date of the funeral. They then make arrangements for the nine days of official mourning and choose the date when the conclave will start. The Particular Congregation also sees to it that the Pope's "Fisherman's Ring" and the lead seal under which Papal documents are dispatched are broken so they cannot be used by anyone else.
The norms to be observed during the "interregnum" while the Throne of St. Peter is vacant were solemnly decreed by Pope Paul VI in his 1975 document, "Romano Pontifico Eligendo" (Election of the Roman Pontiff).
Pope John Paul II updated it in 1996 with an apostolic constitution "Universi Dominici Gregis" (The Shepherd of the Lord's Whole Flock).
The world will know the transition has ended when the dean of the College of Cardinals steps out onto the central balcony of St Peter's Basilica to announce to the crowds in the square "Habemus Papem" ("We have a Pope").
The period is known by a Latin word - interregnum - which means "between the reigns" and reminds the world that the Vatican is one of the world's last absolute monarchies. The power vacuum will last more than two weeks and is filled with a regal pomp and ceremony the Vatican performs to perfection.