The Catholic Encyclopedia is an alphabetical reference work intended to explain Catholic teaching and practice while documenting the Church’s history, institutions, personnel, missions, and intellectual traditions. Its entries range from biblical figures, places, and theological concepts to canon law, papal rulings, councils, dioceses, monasteries, universities, liturgical objects, devotional practices, and sacred art. It discusses doctrines including baptism, angels, atonement, marriage, the immortality of the soul, beatification and canonization, moral action, and papal authority, while recording condemnations of heresies and disciplinary measures concerning clergy, religious orders, and ecclesiastical governance.

In historical and biographical order, the work surveys saints, bishops, theologians, missionaries, scholars, artists, rulers, converts, and founders, emphasizing evangelization, education, charity, martyrdom, reform, and defense of the Church. It traces missions and dioceses across several continents, describes Catholic universities and intellectual achievements, and recounts persecution of Catholics in England. Liturgical and devotional subjects include the Eucharist, altars, fasting, prayer beads, perpetual adoration, the Angelus, sacred music, and the Apostleship of Prayer. A recurring emphasis is critical evaluation: legendary, apocryphal, forged, or disputed traditions are distinguished from better-supported evidence. The concluding material also addresses defensive force, superstition, missionary administration, Augustine’s writings, and controversies involving Gallicanism, Cartesianism, and Jansenism.