With some changes urban legends and murders are better than any script and this story inspired by an urban legend and a series of murders that took place in Montreal is one of the most successful examples.
All well managed by Bob Clark, in a movie shred at its release, but loved by the audience and which overt the year has gained an important place in the cinema history.  
For some it is the spark that created the "slasher" genre and taught directing techniques/narrative, for others it is a source of inspiration for many filmmakers, and for still others, more simply, it is one of the scariest movies of all time (among the fans is said that there were Elvis Presley and Steve Martin).
To wipe out part of the enthusiasm think the same director who defines his film as a "psychological thriller" and not a "slasher". It must also be said that it is difficult to say who invented a genre that owes much (let's say all) to the Italian thriller. And then simply "Black Christimas" is a great slasher that playing with psychology with good ideas used later by other authors.
The winning idea of this movie is to match Christmas with sinister thing, a winning idea with the setting a sorority house.
A sweet and bitter present since the early scenes, with the sorority house that show the Christmas lights but also a gloomy aspect show in a POV by the mysterious killer who sneaks inside.
From here starts the classic boy count (seven is the final bill) with the killer hiding in the attic who phones the victims and with the girls (and some external) ready to be slaughtered. The police at first skeptical and sometimes bizarre character are the extra characters that have become stereotypes of the genre, to which Bob Clark adds several interesting features. Scary and awesome movie for its time has also large doses of black humor that make it even more interesting.
Shot near Toronto is a film that uses very simple means to show the murders. Clark in great shape succeeds and above all is able to manage some changes in important refuse. In fact, Malcolm McDowell and Bette Davis, had to be part of the project, but both give up the role, while John Saxon, the cop, arrives at the last minute. A cast no doubt important that sees names like Margot Kidder (known for her role as Lois Lane), Olivia Hussey (IT, Juliet) and Andrea Martin.
Released at first with the title "Silent Night, Evil Night" (because producers feared it was confused for a "blaxploitation" is a film not to be missed, especially if you doubt about the usefulness of Christmas.