The Week of Prayer for Christian Unity is an international and ecumenical observance kept annually between 18 January and 25 January. It is actually an octave: eight days.

The Week of Prayer for Christian Unity began in 1908, and focused on prayer for church unity. The dates of the week were proposed by Paul Wattson: beginning on the feast of the Confession (or Chair) of Saint Peter on 18 January, and concluding with the feast of the Conversion of Saint Paul on 25 January. In the southern hemisphere, where January is a vacation time, churches often find other days to celebrate the week of prayer, for example around Pentecost (which was suggested by the Faith and Order movement in 1926), which is also a symbolic date for the unity of the church.

In 1948, with the founding of the World Council of Churches, the Week of Prayer for Christian Unity became increasingly recognised by different churches throughout the world.