Churches throughout the world are preparing for next year's Week of Prayer for Christian Unity which will mark the 100th anniversary of the event.

The first time Christians joined in prayer for Christian unity during a week-long celebration bridging the feasts of St Peter and St Paul, was in 1908 in Graymoor, New York, USA.

In the northern hemisphere, 18 to 25 January still is the traditional date for the week of prayer.

Most churches in the southern hemisphere celebrate it around the feast of Pentecost - another symbolic occasion for Christian unity.

"Pray without ceasing" is the theme for the 2008 week. This appeal from the apostle Paul's first letter to the Thessalonians stresses "that prayer is an integral part of the life of Christians precisely as they seek to manifest the unity which is given them in Christ".

These and other explanations concerning the theological and historical background of the week of prayer and its 2008 theme are given in a brochure jointly published and produced by the World Council of Churches Commission on Faith and Order and the Vatican's Pontifical Council for Promoting Christian Unity.

It also includes an outline for an ecumenical service and prayers for the eight days of the week.

Input for the annual brochure comes from Christians in a different country or region each year. For 2008, ecumenical partners from the USA have contributed prayers and other worship resources.

The brochure is now available for download in English, French and Spanish. German and Portuguese translations are to follow.

In the UK resources have traditionally been produced by Churches Together in Britain and Ireland. The organisation is expected to launch its 2008 resources later this year.