In this article the A. tries to trace how the insights of the Second Vatican Council, in particular the Decree on Ecumenism, have been put into service of the search for Christian Unity. In the first part, he seeks to outline those elements of UR which were to engage the whole Church (hierarchy and faithful) in the search for unity. UR numbers 6 (call for continual renewal which is based on a profound conversion), 22 (baptism as the bond of unity among Christians), 3 (the Spirit of Christ uses other Churches as means of salvation), 15 (the Eucharist as means of building up and further grow of the Church of God), 4 (division of the churches inhibits the Church from expressing the fulness of catholicity), and 1 (division not only contradicts the will of Christ but is a scandal to the world and damages the mission of proclaiming the Gospel to every living creature): these elements of the Decree are used to illustrate how the Council saw the Church as engaging in the ecumenical movement. The instruments suggested were study, prayer, reciprocal knowledge of each other, ecumenical formation, collaboration and above all theological dialogue. In the second part of the article, the A. shows how these instruments were used by the Catholic Church in its search to carry out the task given by the Council. Included herein is a brief summary of the results of the major dialogues held thus far. Finally in the last part of the article entitled «Christian Unity and Contemporary Europe», Card. Willebrands shows the role of European culture and history in the process of carrying out the task confided to the churches to seek fulfillment of the will of Christ «that all may be one» (pp. 441-460).