The World Council of Churches (WCC) is a worldwide Christian inter-church organization founded in 1948 to work for the cause of ecumenism. Its full members today include the Assyrian Church of the East, the Oriental Orthodox Churches, most jurisdictions of the Eastern Orthodox Church, the Old Catholic Church, the Lutheran churches, the Anglican Communion, the Mennonite churches, the Methodist churches, the Moravian Church, Mar Thoma Syrian Church and the Reformed churches, as well as the Baptist World Alliance and Pentecostal churches. Notably, the Catholic Church is not a full member, although it sends delegates to meetings who have observer status.

The WCC describes itself as "a worldwide fellowship of 349 global, regional and sub-regional, national and local churches seeking unity, a common witness and Christian service". It has no head office as such, but its administrative centre is at the Ecumenical Centre in Geneva, Switzerland. The organization's members include denominations which claim to collectively represent over 500 million people across the world in more than 110 countries.

Many regional affiliates of the World Council of Churches, such as the Middle East Council of Churches and National Council of Churches in Australia, work for the cause of Christian unity at the domestic level, with member denominations including the Oriental Orthodox Churches, Lutheran churches, Catholic Church, Eastern Orthodox churches, Methodist churches, Anglican Communion, Reformed churches, among others.