This was originally commissioned as a half hour extra on the Blu-ray release of La Nuit du maléfice (1971). It quickly ballooned into the three hour documentary we see today.
This is Canadian film-maker Kier-La Janisse's directorial debut. Prior to this, she was best known for writing "House of Psychotic Women: An Autobiographical Topography of Female Neurosis in Horror and Exploitation Films", considered by many to a key work in the study of female madness onscreen.
A section on music in folk horror films was dropped.
Director Kier-La Janisse is a huge fan of the original The Wicker Man (1973), a film which is referenced frequently in her documentary.
A year and a half into the film's production, Kier-La Janisse realized that editing it herself was too big a job and recruited Benjamin Shearn and Winnie Cheung to help out. (Shearn had to leave after three months because of an unrelated injury.)