Eastern Christianity comprises the Christian traditions and churches that developed in the Balkans, Eastern Europe, Asia Minor, the Middle East, Horn of Africa, India and parts of the Far East over several centuries of religious antiquity. The term is generally used in Western Christianity to describe all Christian traditions that did not develop in Western Europe. As such the term does not describe any single communion or common religious tradition, and in fact some "Eastern" churches have more in common historically and theologically with "Western" Christianity than with one another.

The terms "Eastern" and "Western" in this regard originated with divisions in the church mirroring the cultural divide between the Hellenistic east and Latinate west and the political divide between the weak Western and strong Eastern Roman empires. Because the most powerful church in the East was what has become known as the Eastern Orthodox church, the term "Orthodox" is often used in a similarly loose fashion as "Eastern," although strictly speaking most churches consider themselves part of an Orthodox and Catholic communion.