Theologians have long recognized that the Cappadocian fathers are a valuable resource for contemporary reflection on the Holy Spirit. The modern use of their work, however, tends to reflect only a thin sampling of their many writings; it shows little awareness of their complicated historical situation; and it generally operates on the false assumption that Basil of Caesarea, Gregory of Nazianzus, and Gregory of Nyssa offer but three versions of the same theological project. This article provides a new comparative assessment of Cappadocian pneumatology in connection with larger Trinitarian concerns and with practical matters of spirituality, monasticism, and the role of divine grace in the Christian life. It highlights the distinctive character of each theologian's approach to the Holy Spirit by analyzing their relationships to prior fourth-century traditions, their respective uses of Origen, and their differing stances in the contemporary debates with the Pneumatomachians. It argues that Basil's work on the Spirit is less fully Trinitarian and ascetically weaker than that of the other two, that Gregory Nazianzen offers the most fully Trinitarian and methodologically insightful pneumatology of the three, and that the Holy Spirit plays only a minor role in Gregory of Nyssa's theological and ascetical system. In conclusion, it identifies three key areas in which the Cappadocians can still make a significant contribution to current work on the Holy Spirit.