Accepting the challenge to present an elusive and often abstract doctrine in a fresh and vital way, Aldair I. C. Heron traces the development of the doctrine of the Holy Spirit from the Old Testament to modern times. Following a consideration of the Spirit as revealed in the Scriptures, he examines the patristic and medieval periods and the role of the Holy Spirit in the faith and worship of the church. He then discusses the Reformation and the challenges to Trinitarianism that occurred during that period. He concludes with a penetrating discussion of contemporary questions about the Holy Spirit.