From its inception, the modern ecumenical movement has entailed the twin pursuits of realizing both the unity and the mission of the church. Moreover, mission and evangelism were closely related in twentieth-century ecumenical thought. The main ecumenical institutional structure that advanced the churches’ understanding of mission and evangelism for much of the century was the International Missionary Council, which in 1961 became the Commission on World Mission and Evangelism within the World Council of Churches. By the end of the 1960s, Roman Catholics and evangelical Protestants were also making major contributions to the broader ecumenical understanding of mission and evangelism. Enduring theological achievements including the concept of the missio Dei and the contextualization of theology remain a part of the overall legacy of the ecumenical movement.