This volume presents a new translation of St Basil’s On the Holy Spirit, a classic expression of the Church's faith in the Spirit, and a lasting testimony to the author’s Christian erudition. In the words of St Gregory the Theologian, St Basil’s treatise was “written by a pen borrowed from the Spirit’s store.” This work sets forth the distinction of the divine Persons, and their perpetual communion and conjunction. It talks also about the nature of theological language, and the theological significance of the Church’s tradition of worship and proclamation. Although the book was written for St Basil’s fourth-century contemporaries, its message is valid for all ages.