Ecumenism in common use can refer to two different ideas, either relations with non-Christian or non-Orthodox religious groups or instead it is the teaching that the Orthodox Church is not uniquely the one Church of Jesus Christ but rather one of many branches. The former activity can be of dubious value to some, while the latter is considered a heresy by many. To many in the Orthodox Church, participation in ecumenical relations with other religious groups is often an indication that the teaching regarding the Orthodox Church's non-uniqueness is being promulgated, either openly or surreptitiously.
Between these two ideas is the activity of relating to the non-Orthodox with either the notion of witnessing to them the ancient Christian faith or of pandering to them and making concessions in order to build relations. In the 20th century particularly, some ecumenical activities have drawn sharp criticism from various voices within the Orthodox Church, particularly participation in the World Council of Churches and the National Council of Churches in the US. Those opposing ecumenism are often self-labelled as Traditionalists and may be either within or outside mainstream Orthodoxy, particularly within the Old Calendarist movements, who often regard the New Calendar as being a symptom of "branch theory" ecumenism.
- September 2004 Conference on Ecumenism, held at Aristotle University, Thessaloniki, Greece
- Conclusions of the Conference on Ecumenism
- The Church of Serbia vis-à-vis Ecumenism, by Bishop Artemije of Raska and Prizren
- Contours of Conversion and the Ecumenical Movement, by Hieromonk Alexis (Trader) of Karakallou
- The Consequences of Orthodox Participation in the Ecumenical Movement on the Orthodox Witness to the Heterodox West, by Fr. John Reeves
- The Mystery of Baptism and the Unity of the Church, by Fr. Peter A. Heers