Gerald O'Collins, S.J., is a professor at the Gregorian University in Rome and a prolific writer. He has over 30 books to his credit. Although it's a scholarly book and written for the serious student, this book has much good interesting material. In the first section he discusses the Scriptural Roots including the Old Testament background, history of Jesus , the Trinity according to Paul, and the Trinity in the witness of Luke, Matthew, Hebrews and John. The second section concerns historical developments.The Trinity before Nicaea, then until Constantinople I, on to Aquinas and finally our modern setting. In the third and final section O'Collins discusses the personal existence of the Holy Spirit in contemporary circles, Trinitarian persons and actions and concludes with naming the Trinity and images of the Trinity. He concludes with a hymn about the Trinity. An excellent glossary is available to assist us with terms we don't understand. Detailed numbered notes provides places we may go for more information. I would imagine this book has been used or is being used in classrooms somewhere. It contains so much valuable information.