Much of the scholarship dedicated to the working-class culture of early twentieth-century Wales concerns secular, economic, and political matters. Relatively little attention has been given to religion, despite the fact that the 1904–5 revival brought many thousands into contact with the chapel. This study examines the relationship between the labor movement and the nonconformist chapels, tracing the emergence of a “social gospel,” its main protagonists, and its eclipse by the outbreak of World War II.