A major review of Catholic teaching on the family has been launched by Pope Francis. This review could have far-reaching implications for the Church's attitude to marriage, cohabitation and divorce.
An extraordinary synod, or meeting, of nearly 200 bishops from around the world and a sprinkling of lay Catholics will, for the next two weeks, address the huge gulf between what the Church says on these issues and what tens of millions of believers actually do.
Addressing tens of thousands of believers in St Peter's square on the eve of the synod on Saturday night, Francis said the synod could open the door to a "renewal of the Church and society."
Since becoming pontiff just over 18 months ago, Francis has repeatedly highlighted the "wounds" caused by family breakdown in modern society, while suggesting the Church needs to adapt to this new reality.
"The wounds have to be treated with mercy. The Church is a mother, not a customs office, coldly checking who is within the rules," he has said, in an allusion to the many divorced people, cohabiting couples and single mothers within the ranks of the Church.
Francis underlined where he stands last month by personally marrying 20 Roman couples, some of whom had been "living in sin" prior to their weddings.
- Deep divisions within Church -
In his 18 months in the Vatican, the 77-year-old pope has already taken steps to overhaul the way the Vatican bank and administration are run and has sent out strong signals about the determination of the Church to deal with the issue of clerical sex abuse.
But a reform agenda on social issues could prove much harder to implement because of deep divisions within the Church, Vatican experts say.
Conservatives in the Church hierarchy have already made it clear they will fight any dilution of traditional doctrine.
The Church's view of marriage has come to be seen as increasingly outdated by many in a world where, in some developed countries, nearly one in two marriages ends in divorce and where the notion of the institution itself has been challenged by the global trend towards the legalisation of same-sex weddings.
The bishops gathered in Rome are certainly not about to embrace gay marriage and few Vatican observers expect much, if any, change on questions such as contraception, another area where Catholic teaching contrasts with the daily practice of millions.
But with Francis on the side of reform, the feeling is that the synod process could lead to some highly symbolic changes when it finally reaches conclusions, which is not expected to happen before 2016 at the earliest.
The most notable of these could be a change in the rules to make it possible for Catholics who divorce and then remarry to receive communion.
That has been banned for centuries but critics say the Church's stance is ludicrous given that individuals who have declared their repentance from more serious breaches of the Christian code, including murder or involvement in organised crime, can take communion.
While the Church may not yet be ready to take a step that would amount to a de facto acceptance of divorce in certain circumstances, the discussions could result in steps to make it easier for failed marriages to be annulled.
Another area in which the Church could send out a signal of compassion is by making it clear that priests should be ready to baptise the children of same sex couples, regardless of the doctrinal disapproval of their parents' union.
The synod will also discuss how priests and parishioners can practically help to shore up marriages within their community. Among questions to be addressed on that score is whether the easy availability of pornography in modern society is a factor in family breakdown.