The Holy Eucharist is "the source and summit of all Christian life." The book by Cardinal Walter Casper, a well-known Catholic theologian and President of the Pontifical Council for Promoting Christian Unity, invites the reader to learn more about the meaning of this Sacrament for the life of every Christian and the Church. The author pays special attention to the significance of the Eucharist for the ecumenical dialogue of the churches, for the restoration of the original unity of Christians. The combination of the author's fundamental theological knowledge with many years of teaching experience in German universities, priestly and episcopal ministry in parishes and the Rothenburg-Stuttgart diocese is a special advantage of this book. The Sacrament of Unity: The Eucharist and the Church is Cardinal Casper's second book, published by Spirit and Letter (the first, Jesus Christ, was published in 2008). The book will be of interest to theologians, teachers of theological disciplines, humanities, all those who care about issues of Christian spirituality.