The ritual of the Headless One examined in this Guide has been one of the most important in modern magic for 160 years. Originating in the Magical Papyri, it was published by Charles Wycliffe Goodwin in 1852. It was swiftly adapted by the Golden Dawn and Aleister Crowley, forming the very core of their ritual arsenal. It has received more recent endorsement from the Temple of Set. The rite has borne various titles, such as the Bornless One, Liber Samekh, and the Preliminary Invocation. A key element of what is effective in modern magic, its ancient roots have long remained a closed book. Only a fraction of the papyri were available to the early revival, and long delays prevented later students investigating much further. That the ritual formed part of an important ‘genre’ within that ancient ritual corpus was a fact suspected by few. An important study of the ritual was published in 1991 by Jake Stratton-Kent in No.6 of the long out of print Equinox/BJT. This booklet is a comprehensively revised and updated expansion of that ground-breaking investigation of the ritual of the Headless One.