1 - Cardinals summoned to Rome
The end of John Paul II's papacy has set in motion the centuries-old process of electing a new pope.
The death of a pope is the signal for cardinals from around the world to pack their bags and head for Rome to elect his successor.
Known collectively as the College of Cardinals, they will meet behind closed doors in a centuries-old ritual known as a conclave.
Gathered together in the spiritually uplifting setting of the Sistine Chapel, they will vote in conditions of absolute secrecy.
After the death of a pope, a conclave cannot begin until 15 days have elapsed, and this delay can be extended to 20 days.
This time period was originally intended to allow cardinals from distant lands time to travel to Rome by sea. Today, in the age of jet travel, they will start arriving at the Vatican within hours of the summons.
Funeral rites for the dead pope are to be celebrated for nine consecutive days, with the burial taking place four to six days after death.
During this period, the responsibility for running the Church falls to the cardinals. Most key Vatican appointments lapse. The holders of these top jobs must wait to see if they will be re-appointed - or replaced - by the new pope.
The most important official at this time is a cardinal known as the camerlengo, or chamberlain. It is his job to supervise the whole election process.
During this period the cardinals will begin to discuss - discreetly of course - the merits of likely candidates. They have to agree on the kind of pope they want - and those discussions start in earnest in the days before the election.
The cardinals do not have to choose one of their own number - theoretically any baptised male Catholic can be elected pope - but tradition says that they will almost certainly give the job to a cardinal.
The Vatican talks about the cardinals being guided by the Holy Spirit. But although open campaigning is forbidden, a papal election is still a highly political process.
The coalition-builders have about two weeks to forge alliances. Senior cardinals who may themselves have little chance of becoming pope can still exert a considerable influence over the others.
This is a crucial stage in the election process and a time when every public remark by the cardinals is picked over by Vatican-watchers.