This review of the first posthumous volume by the late Andrew Walls, The Missionary Movement from the West: A Biography from Birth to Old Age, focuses on his account of the background, motives, progress, and theology of the missionary movement from the West and the unanticipated consequence of Christianity’s decline in the West and growth elsewhere. The golden thread Walls seeks to untangle is how and why Christianity, as in its inception, had once again become a non-Western religion by the end of the twentieth century. He portrays the missionary movement as a “despised, semidetached appendix” within the larger framework of European Christendom and its Great Migration and shows how missionaries played a significant role in the unforeseen shift of Christianity’s center from the Global North to the Global South.