Book excerpt: Perichoresis (mutual indwelling) is a concept used extensively in the so-called Trinitarian revival; and yet no book-length study in English exists probing how the term actually developed in the "classical period" of Christian doctrine and how it was carefully deployed in relation to Christian dogma. Consequently, perichoresis is often used in imprecise and even careless ways. This path-breaking study aims at placing our understanding of the term on firmer footing, clarifying its actual usage in relation to doctrines of God, Christ, and salvation in the thought of John of Damascus, the eighth-century theologian, monk, and hymn writer who gave it its historically influential application. Since John summed up a whole theological tradition, this work provides not only an introduction to his theological vision but also to the key themes of Greek patristic thought generally and thereby lays an essential foundation for those who would dig deeper into the present-day usefulness of perichoresis.