Ecumenism or oecumenism mainly refers to initiatives aimed at greater Christian unity or cooperation. It 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. Not to be confused with Nondenominational Christianity

The word contrasts with interfaith dialogue or interfaith pluralism aimed at unity or cooperation among diverse religions and referring to a worldwide 'religious unity' by the advocacy of a greater sense of shared spirituality.

The word is derived from Greek οἰκουμένη (oikoumene), which means "the whole inhabited world", and was historically used with specific reference to the Roman Empire. The ecumenical vision comprises both the search for the visible unity of the Church (Ephesians 4.3) and the 'whole inhabited earth' (Matthew 24.14) as the concern of all Christians.