A small corner of specialist Bonhoeffer scholarship has long-recognised that the musico-theological discussions in his prison letters go beyond simple musings written to a like-minded soul. In recent years Bonhoeffer’s creative use of musical terminology has even sparked a highly constructive resurgence of interest in this adumbrated theology of music. Yet, the full significance of Bonhoeffer’s musical thinking has not been sufficiently actualised. In this context, this thesis offers a re-examination of how Bonhoeffer employs musical patterns of thought and language to a theological end. First outlining Bonhoeffer’s musico-theology and how it has been understood up until now, I set the stage for a closer examination. Through an analysis of Bonhoeffer’s musical metaphor of polyphony as he applies it to the Chalcedonian definition, I am able to demonstrate how his account of Christian formation which is so intimately connected to this Christology, and which polyphony helps to articulate, also contains a latent pneumatology. Showing that the relationship between Christology and Christian formation in his theology is most fully realised by incorporating a pneumatology, I argue that his appeal to polyphony in effect articulates this pneumatology, as an indirect but nevertheless exceedingly successful means of contouring an account of the Spirit’s work. This interrogation of Bonhoeffer’s musico-theology has two main benefits. First, my clarification of Bonhoeffer’s use of polyphony with respect to the Christology it expresses helps to disclose a pneumatology. While only nascent in Bonhoeffer, this pneumatology is arguably vital to understanding his theology of Christian formation in Christ. Second, this examination of Bonhoeffer’s musico-theology opens the way for me to make some suggestions with regard to what musical metaphors, with their capacity to convey dual agency, can offer a theology of the Holy Spirit with respect to Christology.