The article is a topic outline of the theology of the Church’s unity. It shows the spectrum of contemporary reflection on this attribute of the Church mentioned in the Nicene-Con-stantinople Symbol (credo in unam Ecclesiam). The reflection includes biblical categories, especially the idea of koinōnia/communio, emphasizing the Trinitarian basis for unity of the Church, and its concrete means – bonds of unity. Among these means of unity, particular attention is paid to the bond of faith, the sacraments and ecclesiastical governance, nota-bly the universal ministry of Christian unity. Individual Churches (denominations) have different visions of unity, but also these concepts are the subject of ecumenical dialogue. The most recent ecumenical vision on the Church, including its unity, is the document of the World Council of Churches Commission on Faith and Order, Towards a Common Vision of the Church (published in 2013). Christian Churches involved in the contemporary ecumenical dialogue are aware that the unity of the Church is a reality given and set, yet incomplete and imperfect, so to speak “on the way”. In this sense they can express their spero in unam Ecclesiam.