The horror genre is often derided amongst critical circles as a genre not to be taken seriously - like action movies, horror rarely wins prestigious awards, frequently overlooked and rarely falling into the category of "great cinema". To call this unfair would be an understatement - over the years, many horror movies have been produced which display every bit as much skill and mastery of the form as any other type of film, with a particular emphasis on the art of creating tension through atmosphere with all the attendant factors such as production, sound design and judicious editing which goes with it. Of course, some horror movies have proven to be considerably more groundbreaking than others - some push the genre to extremes in ways previously never seen, while others forge a new path and offer up a whole new subgenre of horror which audiences have never seen before. Throughout cinematic history there have been a number of groundbreaking horror movies which fall into this category, many of which are fantastic movies in and of themselves when seen outside the horror genre tag. The following list covers, in chronological order, 20 of the most groundbreaking horror movies of all time - spanning nearly 100 years of motion picture history, these great films changed the shape of horror movies forever.
