The Archbishop of Canterbury will become the first leader of the Church of England to make a pilgrimage to the Roman Catholic shrine of Lourdes this week.
The visit will be made as part of the Church's mission to achieve Christian unity, Lambeth Palace said.
Rowan Williams will preach at the International Mass on Wednesday, which is being celebrated by His Eminence Cardinal Walter Kasper, President of the Pontifical Council for the Promotion of Christian Unity.
His presence at the Shrine of Our Lady of Lourdes in the Pyrenees in France coincides with its 150th anniversary celebrations.
Catholics believe that the Virgin Mary made 18 apparitions to a French peasant girl called Bernadette Soubirous in a grotto in Lourdes in 1858. The shrine has since been visited by millions of pilgrims from across the world.
Dr Williams will participate in the celebrations at the invitation of the Bishop of Tarbes and Lourdes, Monsignor Jacques Perrier. He will also take part in a pilgrimage of bishops, clergy and laity of the Church of England, organised by the Society of Mary and the Anglican Shrine of Our Lady of Walsingham.
He will be accompanied in Lourdes by the Church of England bishop with particular responsibility for chaplaincies in France, the Right Reverend David Hamid, the suffragan bishop of the Diocese in Europe.
His visit follows that of Pope Benedict, who made a pilgrimage to the town last weekend.
The organisers of the 150th anniversary celebrations said that an average of 20,000 pilgrims a day have been visiting the shrine this year.
Many are ill or disabled and believe that the water in the grotto's spring is holy and may cure them.
