In churches and chapels across Wales, as across the world, Christians of various traditions are preparing to meet together for prayer.
It's exactly one hundred years ago this Friday 18 January that the first Week of Prayer for Christian Unity was held through the initiative of two priests, one in England, the other in America. An appropriate time, then, to try to assess just what progress has been made.
There have been many documents, conferences and agreements. Many of the old suspicions have largely disappeared. But the historic Christian denominations remain separate, and lots of new church groupings have developed as well - together with new themes for disagreement.
In this week's All Things Considered, Roy Jenkins asks what of lasting worth has a century of praying for Christian unity produced? And what are the particular ecumenical challenges for the 21st century?
Joining him to discuss the issues are Aled Edwards, Anglican priest and Chief Executive of Cytun, Churches Together in Wales; Keith Clements, a Baptist minister and former General Secretary of the Conference of European Churches; Jonathan Stephen, Principal of the Wales Evangelical School of Theology and Director of Affinity, a group of 1300 conservative evangelical churches; and from New York James Loughran, a Roman Catholic Franciscan Friar from the Graymoor Ecumenical and Interreligious Institute, who is a member of the community where the Week of Prayer for Christian Unity originated.