Where it came from
Eastern Orthodox churches trace their life to the earliest Christian communities, especially those shaped by the Greek-speaking eastern Roman world. They receive the teaching of the first seven ecumenical councils, major gatherings of bishops that addressed Christian belief between the fourth and eighth centuries.
The separation of Eastern and Western churches developed over centuries. The mutual condemnations of 1054 became a landmark in a separation that developed over centuries through disputes about authority and theology, as well as differences of language and politics. Orthodox objections to the pope’s authority over the whole church remain distinct from differences about the Holy Spirit’s relationship to Father and Son; see the Trinity comparison.
What it emphasizes
Orthodox Christians read the Bible within the church’s inherited worship and teaching. Salvation includes forgiveness, liberation from death, and the healing of human life through Christ. A characteristic word is theosis, participation in God’s life by grace. It means becoming like God in holiness and love, while remaining human; it does not mean becoming another independent god.
Icons are sacred images of Christ, Mary, and saints. Orthodox Christians distinguish honoring the person represented from worship, which belongs to God. Their use rests on the conviction that God became genuinely human in Jesus. Prayer, fasting, care for others, and sacramental life belong together.
Worship and organization
The Divine Liturgy is the principal Eucharistic service, usually filled with sung prayer, Scripture, incense, and movement. Orthodox Christians believe that in Communion they receive Christ’s body and blood. The Communion guide compares Christian explanations of this meal.
The family includes self-governing churches, such as the Greek, Antiochian, Serbian, and Romanian churches, led by bishops and councils. The Ecumenical Patriarch of Constantinople has a historic coordinating role described as “first among equals,” rather than the pope’s Catholic role.
Differences within the family
Languages, calendars, local customs, and relationships between church authorities vary. Disputes over jurisdiction and recognition of independence can strain relations; a shared tradition does not remove every institutional disagreement.
National names identify historical communities, not restrictions on who may belong. A visitor may encounter English or another local language alongside older liturgical languages. Asking about the service and rules for receiving Communion helps make unfamiliar worship understandable. Eastern Orthodoxy is a separate communion from Oriental Orthodoxy, despite their similar English names.
Sources & further reading
A question in the margin is a good place to begin.