The Testament of Solomon comprises a family of texts, some dating to the fourth century CE or earlier, relating an extra-Biblical account of King Solomon's divinely-conferred power to constrain the demons who plague the human race. It is also, implicitly, a handbook for those bold or foolhardy enough to follow his example in the demonological sciences. Translated here for the first time from fifteenth-century Byzantine Greek manuscripts, one such text of this secret Solomonic history has finally been made available in English. Along with the unique catalogue of spirit names, sigils, dominions, and offices found in this text - among which readers will discover some genuinely surprising characters - this edition also includes an expository introduction and annotations by the translator which situate the text within its historical milieu, manuscript tradition, and a lineage of magical and demonological theory reaching back to the Greek Magical Papyri. This scholarly analysis, no less than the evidence of the manuscripts themselves, emphasizes that the Testament in all of its forms was first and foremost a work of practical magic.