As the Catholic Church prepares to celebrate on April 27th its first-ever canonization of two popes at the same time, John XXIII and John Paul II, below is a step-by-step guide to the process of achieving full sainthood.
The procedure can be very expensive – costing up to €728,000 – and this has tended to favour candidates from the developed world, although the Vatican is now trying to make it easier for sainthood causes from poorer countries.
In the case of John XXIII, Pope Francis also skipped a traditional step by approving the cause even though no second miracle has been found in a procedure known as "equipollent canonization" which effectively allows for recognition of a candidate's saint-like cult status.
Here's what it takes to become a saint:
1. 'Reputation for sainthood'
Friends or relatives can apply posthumously for their loved one to be recognised as having a "reputation for sainthood", which gets the ball rolling on the full sainthood application process.
This usually begins at least five years after a person's death, although this was not the case for crowd favourites Mother Theresa and John Paul II for whom the timetable has been brought forward.
Once the saintly reputation is recognized, the person in question becomes a "Servant of God" and a "postulator" is appointed to collect testimonies, researching writings to come up with a warts-and-all account of that person's life.
The file is then passed to the Congregation for the Causes of Saints, a Vatican department, where the case must overcome scepticism from a figure tasked with arguing against the candidate's character – the origin of the expression "devil's advocate".
If the Vatican gives the go-ahead, the person is no longer "Servant of God" but considered "Venerable" and the search begins for supposed miraculous healings attributed to their name.
Doctors and theologians are involved in these Vatican in-depth investigations of "miracles" and many candidates are rejected at this stage because other possible causes for the recoveries are found.
If Vatican investigators find evidence of what they believe to be a miracle, then the candidate is "beatified" and can be referred to as "blessed".
The beatification ceremony is usually celebrated by senior clergymen in the candidate's home town and a calendar day for their veneration is assigned.
Many years can pass between the attribution of a first and a second miracle and some sainthood candidates remain forever at the "blessed" stage.
If a second miracle is identified, however, the canonization goes ahead with a mass that can only be celebrated by the pope and held in St Peter's Basilica.