Horror is a film genre seeking to elicit a negative emotional reaction from viewers by playing on the audience's primal fears. Inspired by literature from authors like Edgar Allan Poe, Bram Stoker, Mary Shelley, horror films have for more than a century featured scenes that startle the viewer. The macabre and the supernatural are frequent themes. Thus they may overlap with the fantasy, supernatural, and thriller genres.

Horror films often deal with the viewer's nightmares, hidden fears, revulsions and terror of the unknown. Plots within the horror genre often involve the intrusion of an evil force, event, or personage, commonly of supernatural origin, into the everyday world. Prevalent elements include ghosts, aliens, vampires, werewolves, demons, dragons, gore, torture, vicious animals, evil witches, monsters, zombies, cannibals, and serial killers. Conversely, movies about the supernatural are not necessarily always horrific.

There are many sub genres to horror and these are a few examples:

Action Horror - A subgenre combining the intrusion of an evil force, event, or supernatural personage of horror movies with the gunfights and frenetic chases of the action genre. Themes or elements often prevalent in typical action-horror films include gore, demons, vicious animals, vampires and, most commonly, zombies. This category also fuses the fantasy genre.

Body horror – In which the horror is principally derived from the graphic destruction or degeneration of the body. Other types of body horror include unnatural movements, or the anatomically incorrect placement of limbs to create 'monsters' out of human body parts. David Cronenberg is one of the notable directors of the genre.

Comedy horror – Combines the elements of comedy and horror fiction. The comedy horror genre almost always inevitably crosses over with the black comedy genre. The short story "The Legend of Sleepy Hollow" by Washington Irving is cited as "the first great comedy-horror story".

Gothic horror – Gothic horror is a type of story that contains elements of goth and horror. At times it may have romance that unfolds in the setting of a horror tale, usually suspenseful. Some of the earliest horror movies were of this subgenre.

Slasher film – Often revolves around a psychopathic killer stalking and killing a sequence of victims in a graphically violent manner, mainly with a cutting tool such as a knife or axe. Slasher films may at times overlap with the crime, mystery and thriller genre, and they are not all of the horror genre.