Ecumenism (also oecumenism, œcumenism) refers to initiatives aimed at greater religious unity or cooperation.

In its broadest sense, this unity or cooperation may refer to a worldwide religious unity; by the advocation of a greater sense of shared spirituality across the three Abrahamic faiths of Judaism, Christianity and Islam. Most commonly, however, ecumenism is used in a more narrow meaning; referring to a greater cooperation among different religious denominations of a single one of these faiths.

The word is derived from Greek (oikoumene), which means "the inhabited world", and was historically used with specific reference to the Roman Empire. Today, the word is used predominantly by and with reference to Christian denominations and Christian Churches separated by doctrine, history, and practice. Within this particular context, the term ecumenism refers to the idea of a Christian unity in the literal meaning: that there should be a single Christian Church.

Christian ecumenism and interfaith pluralism

Christian ecumenism, in the narrower sense referred to above, is the promotion of unity or cooperation between distinct religious groups or denominations of Christianity. For some Catholics it may, but not always, have the goal of reconciling all who profess Christian faith to bring them into a single, visible organization, i.e. through union with the Roman Catholic Church. For some Protestants spiritual unity, and often unity on the church's teachings on central issues, suffices.

According to Edmund Schlink, most important in Christian ecumenism is that people focus primarily on Christ, not on separate church organizations. In his book Ökumenische Dogmatik (1983), he says Christians who see the risen Christ at work in the lives of various Christians and in diverse churches, realize that the unity of Christ's church has never been lost (pages 694-700; also his "Report," Dialog 1963, 2:4, 328), but has instead been distorted and obscured by different historical experiences and by spiritual myopia. Both are overcome in renewed faith in Christ. Included in that is responding to his admonition (John 17; also Philippians 2) to be one in him and love one another as a witness to the world. The result of mutual recognition would be a discernible worldwide fellowship, organized in a historically new way (pages 707-708; also Skibbe, A Quiet Reformer 1999, 122-4; Schlink, The Vision of the Pope 2001).

Christian ecumenism is distinguished from interfaith pluralism. Ecumenism in this broad sense is called religious pluralism, as distinguished from ecumenism within a faith movement. Standing against ecumenism is the traditional Orthodox Church which staunchly maintains there is but one church, the historic Orthodox church. Leading the anti ecumenical movement in the 1980s was Fr. John Boylan of the OCA. The interfaith movement strives for greater mutual respect, toleration, and co-operation among the world religions.