A film genre is a motion-picture category based (for example) on similarities either in the narrative elements or in the emotional response to the film (namely: serious, comic, etc.). Most theories of film genre are borrowed from literary-genre criticism. Each film genre is associated[by whom?] with "conventions, iconography, settings, narratives, characters and actors". Standard genre characters vary according to the film genre; for film noir, standard characters are the femme fatale and the "hardboiled" detective; a Western film may portray the schoolmarm and the gunfighter. Some actors acquire a reputation linked to a single genre, such as John Wayne (the Western) or Fred Astaire (the musical). A film's genre will influence the use of filmmaking styles and techniques, such as the use of flashbacks and low-key lighting in film noir, tight framing in horror films, fonts that look like rough-hewn logs for the titles of Western films, or the "scrawled" title-font and credits of Se7en (1995), a film about a serial killer. As well, genres have associated film-scoring conventions, such as lush string orchestras for romantic melodramas or electronic music for science-fiction films.
The term "genre" was used to organize films according to type since the earliest days of cinema. By the 1950s, André Bazin was discussing the concept of "genre" by using the Western film as an example; during this era, there was a debate over auteur theory versus genre. In the late 1960s, the concept of genre became a significant part of film theory.
Film genres draw on genres from other forms; Western novels existed before the Western film, and musical theatre existed before film musicals were made. The perceived genre of a film can change over time; for example, The Great Train Robbery (1903) is seen in the 2010s as a key early Western film, but when it was released, it was seen as related to the "then-popular genres of the chase film, the railroad film and the crime film". A key reason that the early Hollywood industrial system from the 1920s to the 1950s favoured genre films is that in "Hollywood's industrial mode of production, genre movies are dependable products" to market to audiences, they are easy to produce and it is easy for audiences to understand a genre film. In the 1920s to 1950s, genre films had clear conventions and iconography, such as the heavy coats worn by gangsters in films like Little Caesar (1931). The conventions in genre films enable filmmakers to create them in an industrial, assembly line fashion, an approach which can be seen in the James Bond spy films, which all use a formula of "lots of action, fancy gadgets, beautiful woman and colourful villains", even though the actors, directors and screenwriters changed.