The Church is a mystery. Believers who want to enter more deeply into that mystery will reflect on the Church's basic characteristics, the marks of the Church: what it means for the Church to be one, holy, catholic, and apostolic. Non-Catholics and nonbelievers looking to appreciate how Catholics regard the Church also will desire to understand these marks. In this book, renowned Dominican theologian Father Aidan Nichols explores the Church's characteristics. Drawing on insights from four theological masters--Henri de Lubac, Jean Tillard, Hans Urs von Balthasar, and Charles Journet--Father Nichols seeks to help Catholics and non-Catholics to figure out the Church, on at least a fundamental level. Of course the four masters in question do not claim to exhaust the mystery of the Church. Nor does Nichols. They do, however, assist the reader in going deeper into the mystery. To accomplish this goal, Father Nichols appeals to both the Scholastic tradition and authors influenced by the ressourcement movement in theology. In this way, he provides readers with a sense of Catholicism's breadth, which is at once orthodox and yet generously conceived.