In 1982, David B. Barrett released his 1,000-page World Christian Encyclopedia, which presented a comprehensive quantitative assessment of World Christianity for the first time. This book is the first historical project to analyze Barrett's archival materials, which shed light not only on the production of the Encyclopedia, but more importantly, on the development of World Christianity as a discipline and the importance of both African Christianity and quantitative perspectives in its history. This book captures innovations at the intersection of World Christianity, mission studies, and the sociology of religion - the kind of interdisciplinary research that makes World Christianity studies unique.