This study is the first comprehensive history of the impact of the modern missionary movement on the understanding of and work toward Christian unity. It tells stories from all branches of the church: Roman Catholic, Orthodox, and Protestant in its many types (conciliar, evangelical, Pentecostal, and independent). Part 1, Historical, highlights the contribution of modern missions to Christian unity, from William Carey and his antecedents and peers to present-day missions. Part 2, Ten Models of Unity, takes an inductive approach to history, asking not how should Christians cooperate? but how has the missionary movement helped Christians to work together at the local, national, regional, and global level? Part 3, Wider Ecumenism, broadens the evidence to include how the missions movement has helped not only institutional churches but also broader society to have concern for the unity of the entire human family. Included here is the story of how the Protestant missionary movement influenced the forming of the United Nations as well as the drafting of the Universal Declaration of Human Rights. The study also covers the movement’s impact on Christian attitudes toward, and relations with, persons of other faiths. Mission and Unity is the standard reference work in the field for persons studying modern history, modern church history, missions, and ecumenics.