The present article analyses J. Ratzinger's texts on the subject of the Eucharist, focusing on those in which he reflects on the mystery of the Eucharist by discussing its sources. In his texts, the Bavarian theologian attempts to define the essence and permanence of this sacrament describing it as an unshakeable foundation for the Church’s communio. This dimension is examined in the first part of the article. The article further discusses the role that, according to the Bavarian theologian, the Eucharist plays in the life of the Church and how it affects the members of the Mystical Body of Christ. The last part of the article is devoted to the realisation of the Eucharist in the life of Christians and how it builds communio in the community of the Church including the concrete ways indicated by J. Ratzinger in which the Church realizes its communio. The Bavarian theologian, in his reflection on the role of the Eucharist in building the community of the Church, does not restrict himself to purely theoretical reflection but also points out specific ways in which this reality can be realised in the lives of Christians.