Eastern Orthodoxy by country
Based on the numbers of adherents, the Eastern Orthodox Church (also known as Eastern Orthodoxy) is the second largest Christian communion in the world after the Roman Catholic Church. The most common estimates of the number of Eastern Orthodox Christians worldwide is approximately 200–260 million. The numerous Protestant groups in the world, if taken all together, outnumber the Eastern Orthodox, but they differ theologically and do not form a single communion.
Ecumenism
Many theologians of the Eastern and Oriental Orthodoxies engage in theological dialogue with each other and with some of the Western churches, though short of full communion. The Eastern Orthodox have participated in the ecumenical movement, with students active in the World Student Christian Federation since the late 19th century. Most Eastern Orthodox and all Oriental Orthodox churches are members of the World Council of Churches. Kallistos of Diokleia, a bishop of the Eastern Orthodox Church has stated that ecumenism "is important for Orthodoxy: it has helped to force the various Orthodox Churches out of their comparative isolation, making them meet one another and enter into a living contact with non-Orthodox Christians."