Ailing Pope John Paul II receives Archbishop of Canterbury Rowan Williams at the Vatican on Saturday for their first talks since Williams' appointment as spiritual leader of the world's 70 million Anglicans last year.
Their meeting comes amid a damaging row within the Anglican church over the ordination of gay priests, an issue which has caused as much consternation within the Vatican.
Talks between the pope and Williams also come ahead of the 25th anniversary of John Paul's ascension to the papal throne.
Aged 83, the pope is crippled by a combination of Parkinson's disease and arthritic complaints.
One his most senior lieutenants, Cardinal Joseph Ratzinger, took the unprecedented step this week of discussing the pontiff's poor health with a German magazine amid fears it was deteriorating.
Despite fundamental doctrinal differences, the Anglican and Roman Catholic churches have enjoyed an amicable relationship stretching back a number of decades.
"Given the historical relations of the two churches, the simple fact that there are regular visits of archbishops to the Holy See is exceptional," a Church of England spokesman told AFP this week.
"We want to build up on the excellent relations," he said ahead of Williams' visit that begins Friday through Sunday.
Williams' predecessor George Carey was a regular visitor to the Vatican while Pope John Paul, head of some one billion Roman Catholics, has made just a single visit to Britain, in 1982.
Following his talks with the pope, Williams will visit the tomb of Saint Peter. Williams will use the occasion to invest bishop John Flack, his representative at the Vatican.
Williams' visit comes ahead of an emergency summit of Anglican bishops from around the world to discuss gay ordination -- an issue that has threatened to split his church down the middle.
The summit, called by Williams and to take place in London in mid-October, comes after the confirmation of openly gay cleric Gene Robinson as Episcopal bishop of the US state of New Hampshire earlier this year.
Williams, who took office as Archbishop of Canterbury in February following his appointment last year, is known for his liberal views and his support -- in principle -- for the appointment of gay clergy.
He raised no objection to the appointment in July of the openly gay Canon Jeffrey John as bishop for the British town of Reading. John later withdrew his candidacy to avert a schism between conservative and liberal factions within the Church of England.
"It wouldn't be appropriate for us to get involved in any way in the internal debate of the Church of England on homosexuality," a spokesman for England's Roman Catholic Church said this week.
He added that Williams' talks with the pope would likely focus on areas of common ground, such as doubts over the Iraq war and bioethics.