Ecumenism broadly refers to movements between Christian groups to establish a degree of unity through dialogue. Ecumenism is derived from Greek οἰκουμένη (oikoumene), which means "the inhabited world", but more figuratively something like "universal oneness." The movement can be distinguished into Catholic and Protestant movements, with the latter characterised by a redefined ecclesiology of "denominationalism" (which the Catholic Church, among others, rejects).

Over the last century, moves have been made to reconcile the schism between the Catholic Church and the Eastern Orthodox churches. Although progress has been made, concerns over papal primacy and the independence of the smaller Orthodox churches has blocked a final resolution of the schism. On 30 November 1894, Pope Leo XIII published Orientalium Dignitas. On 7 December 1965, a Joint Catholic-Orthodox Declaration of Pope Paul VI and the Ecumenical Patriarch Athenagoras I was issued lifting the mutual excommunications of 1054.