The idea for The Penguin Book of Demons belongs to my editor, John Siciliano, who has been a supportive collaborator in my writing for Penguin Classics for the past decade. Professor Paul Cobb (University of Pennsylvania) curated chapter 5 on the Islamic jinn, and Professor Richard P. H. Greenfield (Queens University) wrote the introductions and rendered the translations in chapter 6 on the Byzantine Gellou. I am grateful to them both for their expertise. Three PhD candidates in history at Fordham University provided assistance as well. Benjamin A. Bertrand and W. Tanner Smoot translated some of the medieval Latin texts. They also proofread the manuscript with great care alongside Amanda Racine. I appreciate their help and camaraderie. Anne, Mira, and Vivienne heard many of these stories about demons at the dinner table. Their patience with my infernal pursuits has been nothing less than heroic.