Catholic Encyclopedia: Sts. Cyril and Methodius: Also called Constantine and Methodius. Biography of these ninth-century brothers, Apostles of the Slavs.
Catholic Online: Sts. Cyril and Methodius: Reflection on their lives.
Cyril and Methodius, Missionaries to the Slavs: Outline of their missionary activities. With prayer in traditional and contemporary language.
Cyril and Methodius, Saints: Short note on the fathers of Slavonic literature, in the Columbia Encyclopedia.
Cyril, Monk, and Methodius B: Illustrated biography of SS. Cyril and Methodius.
Grande Munus: Encyclical of Pope Leo XIII, on SS. Cyril and Methodius, promulgated in 1880.
Lives of the Saints: SS Cyril and Methodius: From Alban Butler's Lives of the Saints.
Slavorum Apostoli: Commemoration of the Eleventh Centenary of the Evangelizing Work of SS. Cyril and Methodius. Encyclical of Pope John Paul II, promulgated in 1985.
St. Cyril and St. Methodius: The story of these two brothers, suitable for children. Preformatted line breaks can make this difficult to read.