The "Apostles to the Slavs" who brought Christianity and literacy to Slavic peoples in the 9th century. Celebrated on May 11th, these brothers created the Glagolitic alphabet and translated the Bible and liturgy into Old Church Slavonic. Their missionary work established Orthodox Christianity among the Bulgarians, Moravians, and other Slavic nations.

The central worship service of the Orthodox Church, celebrating the Eucharist (Holy Communion). Usually celebrated on Sundays and feast days, the Divine Liturgy consists of the Liturgy of the Word (scripture readings) and Liturgy of the Faithful (Eucharistic prayer and communion). The most common forms are the Liturgies of St. John Chrysostom and St. Basil the Great.

The morning prayer service of the Orthodox Church, traditionally celebrated at dawn. Also called Orthros in Greek tradition, this service includes the reading of the Gospel, the Great Doxology, and numerous psalms and hymns. Matins prepares the faithful for the day and is often celebrated immediately before the Divine Liturgy on Sundays and feast days.