O Círculo Católico de Operários de Barcelos (Barcelos Catholic Workers’ Circle) is a Catholic organization of factory and shop workers set up in 1903 to keep workers Catholic, and to combat the socialist and republican secularism and anticlericalism spreading in Portugal since the last quarter of the 19th century. This book stems from research for a master’s degree in 2005 in the History of Ideas and Modern and Contemporary Culture, at the Social Sciences Institute, University of Minho, Braga, Portugal.