Orthodox Protestants and Roman Catholics in the northern hemisphere join Friday for one week to pray together for a week of Christian unity.

The Week of Prayer for Christian Unity is traditionally celebrated between January 18-25 (in the northern hemisphere) or at the feast of Pentecost (in the southern hemisphere).

On Monday, the Holy See will host an Interreligious Service at the chapel of the Ecumenical Center at which the Permanent Representative of the Holy See to the United Nations, Monsignor Sivlano Tomasi, will lead the prayers.

Also giving submissions during the service at the Ecumenical Centre, which is the headquarter of the World Council of Churches, will be WCC General Secretary, the Rev. Olav Fyske Tveit and leaders from the Buddhist, Jewish and Muslim communities in Geneva.

The Monday service springs from the World Day of Peace and has for the past two years been held on the week when Christian churches and denominations pray for unity.

The Catholic-led service is held during the Week of Prayer which enters into congregations and parishes all over the world. Pulpits are exchanged, and special ecumenical celebrations and prayer services are arranged.

The Week of Prayer for Christian Unity has for more than 40 years been jointly prepared by the World Council of Churches Commission on Faith and Order and the Catholic Church's Pontifical Council for Promoting Christian Unity.

The WCC representing Anglican, Orthodox and Protestant Christians was founded after the Second World War. It has 349 churches and denominations representing more than 560 million Christians. Its main goal is Christian unity.

The Roman Catholic Church is not a member of the WCC. It however cooperates with the council on many issues, serving on its faith and order body as well as collaborating on many levels with WCC partners such as the ACT Alliance that dealins with disasters and development.