Organizing the laity to participate in a dynamic way in the mission of the (Roman) Catholic Church. Classically: organizing the participation of the laity in the apostolate of the Catholic Churches hierarchy. The concept is broad, and can refer to any external action of a Catholic layman inspired by his faith or only such actions of lay groups as have been so defined and mandated by the local bishop.
The term "Catholic Action" is a literal translation of the Italian "Azione Catholica", a specific national organization or movement. Saint Pius X was the first Pope to use the term, but Pope Pius XI gave to it its classical definition in the encyclical "Ubi Arcano Dei" in 1922. Various Catholic Action movements and organizations, especially in Europe, have their roots in the social awakening of the late 19th and early 20th centuries as a response to the social upheavals of the industrial revolution. The most outstanding practitioner was Canon Joseph Cardijn of Belgium, who was elected to the College of Cardinals in 1965 by Pope Paul VI.
Catholic action has taken varied forms in different countries. It may take the form of broad lay organizations aimed at improving Church-government relations and reviving Catholic practice among the negligent. It may be applied in small groups organized in specialized apostolates concerned with changing or Christianizing economic and social institutions. Or it may be organized around specific tasks such as religious teaching, public moral issues, or community development.