This book examines the rise of anti-Catholic hostility in early nineteenth-century Vietnam under the Nguyen dynasty. French missionaries have long been blamed for the destabilization of dynastic Vietnam and the anti-Catholic violence that preceded the French invasion in 1858. But the focus on the political conflict leading to the Nguyen court's antipathy to the church overlooks the significance of Catholicism as a popular religion. Focusing on, but not limited to, the Cochinchina region, this study explores grassroots experiences of the religion and the conflict between the Nguyen court and missionaries of the Missions Étrangères de Paris (MEP). To do so, it draws on the correspondence of French missionaries and Vietnamese priests from the MEP archive, and on vernacular Vietnamese translations of the Nguyen dynastic record, to provide a new perspective on Nguyen Vietnam from the 1820s to the 1860s.