The mysterious name “IAO” has for centuries been a ubiquitous feature of magical traditions. Many modern systems ascribe this name to Tiphareth and the solar mysteries. However, in the Ogdoadic Tradition of High Magick this name is employed as the divine name of the Moon-sphere, Yesod. The Lunar Formula of IAO discusses the practical magical application of this elusive formula, presenting never-before published keys thereto. While this guide conducts its survey within the milieu of the Ogdoadic Tradition, and provides a brief introduction to the Ogdoadic mysteries as a whole, it will also prove valuable to initiates and students of other traditions of the Magical Art who may find herein a resonance with their own Work.