What is the Goetia? By far, the most widely used "phonebook" of demons is the Goetia. You'll discover a wide range of different spirits here, all with their own personalities and motivations, whether it's to master an instrument, amass a fortune, find true love, or win a battle. The Goetia is part of a larger text called The Lesser Key of Solomon, which is a collection of medieval grimoires that are often said to have been written by King Solomon.