By David Willey
BBC Rome correspondent
Archbishop of Canterbury Rowan Williams, the leader of the worldwide Anglican Communion, is due to arrive in Rome to meet Pope Benedict XVI.
His six-day stay in Rome marks the 40th anniversary of the ground-breaking visit of his predecessor Michael Ramsey to the Vatican.
But the prospects of a return to full communion between the Anglican and Roman Catholic Churches remain dim.
Prospects of a return to full communion remain dim
There will be plenty of occasions for polite, even cordial, exchanges during the coming week between high-ranking Vatican officials and the archbishop and his 10-strong delegation from Lambeth Palace in London.
To emphasise the importance that the Roman Catholic Church in England attaches to the occasion, Cardinal Cormac Murphy O'Connor, the Archbishop of Westminster, is accompanying the Archbishop of Canterbury on his visit to Rome and he will be present at many key meetings and services of prayer.
Although the two Churches have maintained a theological dialogue in recent decades, they remain deeply divided on some substantive issues which still separate them - the consecration of women as bishops is a prime example.
The first woman primate of a Church in the Anglican Communion, Bishop Katharine Jefferts Schori, of the American Episcopal Church, took office in the United States earlier this month.
The position of the Pope is that hopes of restoring communion between Anglicans and Catholics have already been damaged by the decision of Churches within the Anglican communion to ordain women as priests.
The consecration of women bishops puts off the day when Catholics and Anglicans can share worship even further into the future.
Archbishop Rowan Williams and Pope Benedict have one thing in common. They are both distinguished academics, and are both respected Christian theologians.
Pope Benedict will see the archbishop only once
The Pope speaks fluent English and they will be able to have a fertile exchange of ideas when they meet at the Vatican on Thursday.
However Cardinal Walter Kasper, the president of the Vatican's council for promoting Christian unity, who will play a prominent role in many of this week's meetings, has already warned the Church of England that the goal of "full communion" cannot be reached if they decide to follow the American Episcopal example and go ahead with plans to consecrate women as bishops.
Pope Benedict will see the Archbishop of Canterbury only once during the Anglican leader's six-day visit.
The rest of the archbishop's timetable includes two public lectures, a joint prayer service in the Catholic Church of Saint Mary above Minerva (one of Rome's few Gothic-style churches, built over the ruins of a Roman temple), at which Cardinal Kasper will be one of the preachers, and a dinner hosted by Britain's ambassador to the Vatican, Francis Campbell.
Pope Benedict leaves Rome next week for a five-day visit to Turkey.
His priorities at the moment lie more with his uneasy relationship with the Islamic world, and with the Orthodox, another important branch of Christendom.
Seen from Rome, the headquarters of the worldwide Catholic Church, this first extended visit of the head of the Anglican Communion to the Vatican is a relatively low-key event, unlikely to lead to any radical changes or to the reunification of the Churches at any time in the near future.