Häxan explores the roots and superstitions surrounding witchcraft, beginning in the Middle Ages through the 20th century. Based partly on Christensen's own study of the Malleus Maleficarum, a 15th-century German guide for inquisitors, the film proposes the notion that such witch hunts may have stemmed from misunderstandings of diseases and mental illnesses.

After finding a copy of the Malleus Maleficarum in a Berlin bookshop, Christensen spent two years—from 1919 to 1921—studying manuals, illustrations and treatises on witches and witch-hunting. He included a lengthy bibliography in the original playbill at the film's premiere. He intended to create an entirely new film rather than an adaptation of literary fiction, which was the case for films of that day.

Christensen obtained funding from the large Swedish production company Svensk Filmindustri, preferring it over the local Danish film studios, so that he could maintain complete artistic freedom. He used the money to buy and refurbish the Astra film studio in Hellerup, Denmark. Filming then ran from February through October 1921. Christensen and cinematographer Johan Ankerstjerne filmed only at night or in a closed set to maintain the film's dark hue. Post-production required another year before the film premiered in late 1922. Total cost for Svensk Film, including refurbishing the Astra Film Studio, reached between 1.5 and 2 million kronor, making Häxan the most expensive Scandinavian silent film in history.

Häxan has become regarded by critics and scholars as Christensen's masterpiece.  It is listed in the film reference book 1001 Movies You Must See Before You Die, which says "Part earnest academic exercise in correlating ancient fears with misunderstandings about mental illness and part salacious horror movie, Häxan is truly a unique work that still holds power to unnerve, even in today's jaded era."

After finding a copy of the Malleus Maleficarum in a Berlin bookshop, Christensen spent two years studying manuals, illustrations and treatises on witches and witch-hunting. 

The Soundtrack

Caspervek's Soundtrack for Häxan was premiered in February 2015 at the National Art Museum of Tallinn (Estonia) for the band's regular line-up. After years of silence, in 2019, Brais González rewrote the score to add accordion, premiering it again at the Vicente Risco Foundation in Allariz that autumn. The new music includes elements of contemporary music and new musical languages and also many references to medieval music and Gregorian chant.