The current grafting of the international Missionary Council to the World council of Churches has created the need which this book fulfills, of explaining the significance of the merger. The President of Union Theological Seminary is fully quailed to do this since this membership on the Joint Committee has, given him a ringside sat on the years of negotiation and discussion which led to the merger. He reviews the east of the ecumente movement as the spiritual and mental child of the missionary extension of the Christian Church in the 19th and early 20th centuries. The same men were often leaders in both the mission endeavor and the ecumenical movement. They went separate until the time seemed for unity. That unity brings as grave problems as it answers. Dr. Van Dusen has brought these into sharp focus and challenged believers to towards their solution. This book is vital as an interpretation at a time when critical decisions are being made and contributes to a grass roots movement to strengthen unity. Dr. Van Dusen writes well and this book should prove a standard reference for anyone concerned in studying the mission field or the emerging unity of the Church.