What should a Reformed pastor make of ecumenism? The article addresses this by considering the biblical foundation of ecumenism, from the time of Abraham, Isaac, and Jacob, and further worked out in redemptive history. Biblical ecumenism is based on salvation through grace alone. The historic Protestant conception of ecumenism is compared with the modern Protestant conception of ecumenism, which has been influenced by the philosophies of Immanuel Kant, Friedrich Schleiermacher, and Karl Barth. Neo-orthodoxy and its great emphasis on the ecumenical movement is also discussed.