The background of Vatican II’s pastoral and missionary concerns cannot be separated from what is arguably the Council’s most unexpected and far-reaching document, Nostra Aetate, the Declaration on the relationship of the Church to non-Christian religions. While very often interpreted as changing, not to say reversing, traditional Church-centred soteriology, this chapter argues that Nostra Aetate needs to be understood primarily as an event, a moment of self-understanding on the part of the Church which provokes a radical conversio morum. By calling the Declaration the ‘moral heart of the Council’, the chapter focusses specifically on its original purpose. That the Declaration has opened up a broader interreligious perspective to which all the major religions of the world can relate is testament less to the power of particular theological ideas than to its central conviction that the Church finds its own origins not apart from but through the faith which it shares with the people of the Sinai Covenant.