This thesis exposes, from the thought of Joseph Ratzinger, the relationship between the Eucharist and the Church, in order to delve into the totality and unity of this author s theological production. In this relationship, it can be seen that the Eucharist builds the Church and that the celebration of the Supper in the ecclesial community is the core element of this mystery. Ecclesiology, understood from its relationship with the Eucharist, was a unique reference in the understanding of J. Ratzinger. For him, the Church can be defined as the people who live from the Body of Christ and who, in the Eucharist, themselves become the Body of Christ. The Church is, fundamentally, communio sanctotum, in the double sense of communion of the goods of salvation (sancta) and communion of those who receive this good (sancti). In this way, the analytical exposition of J. Ratzinger s production leads to the junction of theses - synthesis - influenced mainly in the applications of the decisions of the Second Vatican Council, as well as great thinkers such as De Lubac, Congar, Tillard, Forte, Kasper, Zizioulas, great promoters of a Eucharistic ecclesiology or of communion.