Eastern Christianity consists of four main church families: the Eastern Orthodox Church, the Oriental Orthodox Churches, the Assyrian Church of the East, and the Eastern Catholic Churches. The term is used in contrast to Western Christianity. Collectively they comprise the Christian traditions and churches that developed in the Balkans, Eastern Europe, Asia Minor, the Middle East, Africa, India and parts of the Far East over several centuries. The term does not describe a single communion or common religious tradition. Some Eastern churches have more in common historically and theologically with Western Christianity than with one another. The various Eastern churches do not normally refer to themselves as "Eastern", with the exception of the Assyrian Church of the East and its offshoots.

The terms "Eastern" and "Western" in this regard originated with geographical divisions in the Christian 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 largest church in the East is the body currently known as the Eastern Orthodox Church, the term "Orthodox" is often used in a similarly loose fashion as "Eastern", to refer to specific historical Christian communions. However, strictly speaking, most Christian churches, whether Eastern or Western, consider themselves to be "orthodox" (following correct beliefs) as well as "catholic" (universal), even when they do not include those words in their official names.