The boggart was a much-feared, little-studied supernatural being from the north of England. Against the odds, it survives today, whether in place-names or in works of fantasy literature - not least Harry Potter. Centring on this mercurial and mysterious figure, The Boggart pioneers two methods for collecting folklore: first, the use of hundreds of thousands of words on the boggart from digitised ephemera; second, about 1,100 contemporary boggart memories that derive from social media surveys and personal interviews relating to the interwar and postwar years. Through a radical combination of this new information and an interdisciplinary approach - involving dialectology, folklore, Victorian history, supernatural history, oral history, place-name studies, sociology and more - it is possible to reconstruct boggart beliefs, experiences and tales. The boggart was not, as we have been led to believe, a 'goblin'. Rather, this was a much more general term encompassing all solitary, and often ambiguous, supernatural beings, from killer mermaids to headless phantoms to shape-changing ghouls. The author reveals that in the same period that boggart beliefs were dying, folklorists continually misrepresented it, and explores how the modern fantasy was born of these misrepresentations. As well as offering a fresh reading of a deep seam of folklore, this book showcases some of the ways in which harnessing recent advances in digitization can offer rich and compelling rewards.