WEEK OF PRAYER FOR CHRISTIAN UNITY

is an international Christian ecumenical observance. It is an observance lasting eight days.

The Week of Prayer began in 1908 as the Octave of Christian Unity, and focused on prayer for church unity. The dates of the week were proposed by Father Paul Wattson, co-founder of the Graymoor Franciscan Friars. He conceived of the week beginning on the Feast of the Confession of Peter, the Protestant variant of the ancient Feast of the Chair of Saint Peter, on January 18th, and concluding with the Feast of the Conversion of Saint Paul on January 25th.

Pope Pius X officially blessed the concept, and Benedict XV encouraged its observance throughout the entire Roman Catholic Church. For a while, the observance was re-named the "Chair of Unity Octave" by Wattson, in order to emphasize the relationship between Christian unity and the Petrine. From Wikipedia