AbstractThis is the text of the address given by Willem A. Visser 't Hooft to the Uppsala Assembly of the World Council of Churches (WCC) in 1968 after being named honorary president of the WCC, following his retirement as general secretary two years earlier. In this address, Visser 't Hooft reviews the 20th‐century history of the ecumenical movement and the contemporary mandate of the WCC, in which the central issue is the relationship between the church and the world, where the vertical dimension to God of the church's unity determines the horizontal dimension of its service to the world. The address concludes with four challenges: no horizontal advance without vertical orientation; the ecumenical movement and the churches need each other; church unity is important; and youth expects answers.