Like the Western Church, the liturgical practices of the Eastern Orthodox Church were founded on the practices of the mother Church in Jerusalem. This is the liturgical form that spread throughout the Mediterranean basin in the first few years of Christianity, and throughout the known world in the century that followed. The common language and musical forms of the Roman Empire were Greek. Not only did this form the foundation, but in those countries and cultures that retained both Greek language and culture over time, Greek became normative. While the language of Italy changed to Latin, of France to Gallic, and of the British Isles to Anglo-Saxon (and then English), most of the Orthodox countries retained Greek. This provided a living continuity back to the original liturgical form of the early Christian Church.
Among the most striking things about the liturgical worship of the Eastern Orthodox Church is the uniformity of its form, and the high degree of correspondence to the form that was in practice across the Christian Church in the sixth century. The Eastern Orthodox Church has experienced no Reformation that transformed the theological foundation of the faith as well as essentially doing away with the liturgical form and music, as has almost all of Protestantism. Neither has Orthodoxy experienced a twentieth century council that modified both the liturgical form and music, as has the Roman Catholic Church. While the liturgical form did undergo change in the fourth and fifth centuries to reflect the theological maturity of the faith, it still retains a high degree of similarity to early Christian practice.
During the period of the fourth to sixth centuries, the shape of the Eastern Divine Liturgy reached its final form under the guidance of liturgists such as St. John Chrysostom. In this same period the major formative changes occurred, most of which resulted in liturgical components that corresponded to the Church's developing theological understanding. Among them were the hymn "Only-Begotten Son" and the addition of the Nicean-Constantinopolitan Creed (countering heresies), and "The Trisagion Hymn" reflecting the Trinitarian theology being currently defined. (See Sacred Sample) In this period and on through the ninth century, hymns were composed and added to the Divine Liturgy, such as the Cherubic Hymn, sung while the priest recites the prayer that is now called "The Prayer of the Cherubic Hymn." (See Sacred Sample)
Generally speaking, the worship of the Orthodox Church has always been in the vernacular: that is, the local or indigenous language. The best example is Sts. Cyril and Methodius, two Greek missionaries to Russia in the tenth century. They created an alphabet, now called Cyrillic, and translated the Bible and liturgical texts into the native language. While the worship services are the same throughout the Orthodox Church (that is, the theology and liturgical texts are the same), what is different is the language, culture and music. Music is an expression of culture, and two main musical and liturgical traditions have developed over the past 2000 years: Byzantine and Russian. There are also unique liturgical music forms in the Armenian, Georgian and Coptic Orthodox Churches, but the majority of Orthodox Christians follow either the Byzantine or Russian forms.
Byzantine music has pre-Christian origins in Greek music, and is based on modes and chords described by Pythagoras. The early Christian Church spoke Greek, and the common music forms of the Roman Empire were also Greek. A liturgical music form developed over the first few centuries of Christianity which relied on Jewish Synagogue chant and psalmody, and the addition of new material using Greek music theory to create a musical form that was beautiful and appropriate to praise and worship God the Holy Trinity. The earliest hymn we know of is "O Gladsome Light," sung every evening at Vespers, which was referred to by St. Justin the Martyr in 150 A.D.
This new musical form was called Byzantine. Byzantine music, like its ancient Greek predecessor, is characterized by eight modes that are sub-divided into three genres of feeling: Enharmonic, Chromatic and Diatonic. Each mode conveys the feeling associated with the prayer being offered or the text being sung: grave (as in Holy Week); sad or lamentful (as in Christ's passion); or joyous (such as the Resurrection or major feasts). The eight scales do not correspond directly to the major and minor scales of western music, and are characterized by many more semitones, or sub-divisions within a scale. This gives Byzantine music its haunting and somewhat foreign sound, but also allows it to convey so accurately different emotions or feelings.
Byzantine music developed over the first millennia a sophisticated form of chant and a very large body of liturgical material for all the services of the Church. It is principally characterized by melody (vs. harmony or polyphony) to convey the meaning or intent of the prayer or text, antiphonal (responsive) singing, and the use of Byzantine modes. During this period, besides the creation of a musical corpus for all the services of the Church year, masterful forms such as the Kontakion and Kanon were created. Also, great Church musicians such as St. Andrew of Crete, St. Romanos the Melodist, and St. John of Damascus lived and worked. Byzantine music uses a unique "analog" notation, and has gone through several phases (ancient, medieval and late) and refinements. The most recent refinement was the simplification of the notation in 1881.
The Russian music tradition began with the introduction of Byzantine music brought by Greek missionaries in 988 A.D. The earliest forms of "Russian" liturgical music were Znamenny and Kievan Chant, both of which are quite Byzantine sounding. Bulgarian chant is late-Byzantine in style, and quite unique. The type of liturgical music generally thought of as "Russian" began its development as simple polyphony in the seventeenth century under the influence of Polish religious vocal music. It was further enhanced under Peter the Great, who brought to Russia many Western European cultural influences among them musical styles. This is why Russian liturgical music sounds so much more accessible to the Western ear: it uses the same musical theory as Western music.
Most Russian liturgical music is in the major scale (some in the minor scale), with the typical tonal intervals. The introduction of these German, French and Italian music traditions had a lasting influence on Russian Church music, and elevated it to the levels of polyphony and harmony we know today. Much of the Slavonic-speaking Orthodox Church (Serbian, Bulgarian, Albanian, etc.) follows the Russian music traditions. These music traditions were brought to North America in the nineteenth century by Russian missionaries to Alaska and the West coast.