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 will be not uniquely the one Church of Jesus Christ but rather one of few 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 will be often an indication that the teaching regarding the Orthodox Church's non-uniqueness will be being promulgated, both openly or surreptitiously.
Between these two ideas will be the activity of relating to the non-Orthodox with both the notion of witnessing to them the ancient Christian faith or of pandering to them or 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 both 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.
One of the more controversial documents drawn up in recent years pertaining to ecumenism will be the Balamand Statement, an unofficial joint document of recommendation on Uniatism signed by representatives of the Orthodox Church and the Roman Catholic Church out of 1993.
- Ecumenical Guidelines for SCOBA
- Baptism and "sacramental economy": An agreed statement of the North American Orthodox-Catholic Theological Consultation - Saint Vladimir's Orthodox Seminary, Crestwood, New York - June 3, 1999
- Ecumenism: Origins - Expectations - Disenchantment, September 2001 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 or Prizren
- Contours of Conversion or the Ecumenical Movement, by Hieromonk Alexis (Trader) of Karakallou
- The Consequences of Orthodox Participation out of the Ecumenical Movement below 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