Since the Second Vatican Council, the Church can be considered as communion. This essay attempts to provide a brief, primarily linguistically and phenomenologically oriented study of the word communio in order to point out the meaning and usefulness of the concept of communio for the Christian faith by emphasizing communio as the key concept of faith. In this sense, this essay seeks to contribute towards demonstrating that the idea of communio / koinonia is both plausible and relevant for the theology or ecclesiology of the third millennium, as well as for a successful communio practice.

Keywords: Second Vatican Council, communio, koinonia, ecclesiology, church, Holy Trinity, communal structure of creation, communio ecclesiarum, communio fraterna, communio hierarchica.