the organized work of the laity that is performed under the direction or mandate of a bishop in the fields of dogma, morals, liturgy, education, and charity. In 1927 Pope Pius XI gave the term its classical definition as “the participation of the laity in the apostolate of the hierarchy.”

A distinction is normally made between general and specialized Catholic Action. General Catholic Action organizations, such as the Holy Name Society or the Legion of Mary, are open to all Roman Catholics, or at least all of a given age. Specialized Catholic Action groups are limited to members of a given profession or interest group, such as workers, students, doctors, lawyers, or married couples. The most famous of the specialized groups is the Jocists (Jeunesse Ouvrière Chrétienne; in English-speaking nations called the Young Christian Workers), founded in Belgium after World War I as an organized association of factory workers by Father (later Cardinal) Joseph Cardijn.

Besides Catholic Action in the strict sense, in which it is conceived as an extension of the hierarchy, there is the broader notion of the lay apostolate, which involves the more autonomous activity of the laity in the temporal society to bring a Christian influence to their environment. It is this latter notion, which gives greater recognition to the responsibility of the laity, that has been emphasized since the second Vatican Council (1962–65).