The term film noir (French for "black film"), first applied to Hollywood movies by French critic Nino Frank in 1946, was unknown to most American film industry professionals of the era. Cinema historians and critics defined the canon of film noir in retrospect; many of those involved in the making of the classic noirs later professed to be unaware of having created a distinctive type of film.

Problems of definition

Film noirs embrace a variety of genres, from the gangster film to the police procedural to the so-called social problem picture, and evidence a variety of visual approaches, from meat-and-potatoes Hollywood mainstream to outré. While many critics refer to film noir as a genre itself, others argue that it can be no such thing. Though noir is often associated with an urban setting, for example, many classic noirs take place mainly in small towns, suburbia, rural areas, or on the open road, so setting can not be its genre determinant, as with the Western. Similarly, while the private eye and the femme fatale are character types conventionally identified with noir, the majority of film noirs feature neither, so there is no character basis for genre designation as with the gangster film. Nor does it rely on anything as evident as the monstrous or supernatural elements of the horror film, the speculative leaps of the science fiction film, or the song-and-dance routines of the musical.

A more analogous case is that of the screwball comedy, widely accepted by film historians as constituting a "genre"—the screwball is defined not by a fundamental attribute, but by a general disposition and a group of elements, some (but rarely and perhaps never all) of which are found in each of the genre's films. However, because of the diversity of noir (much greater than that of the screwball comedy), certain scholars in the field, such as film historian Thomas Schatz, treat it as not a genre but a "style." Alain Silver, the most widely published American critic specializing in film noir studies, refers to it as a "cycle" and a "phenomenon," even as he argues that it has—like certain genres—a consistent set of visual and thematic codes. Other critics treat film noir as a "mood," a "movement," or a "series," or simply address a chosen set of movies from the "period." There is no consensus on the matter.

The prehistory of noir

Film noir has sources not only in cinema but other artistic media as well. The low-key lighting schemes commonly linked with the classic mode are in the tradition of chiaroscuro and tenebrism, techniques using high contrasts of light and dark developed by 15th- and 16th-century painters associated with Mannerism and the Baroque. Film noir's aesthetics are deeply influenced by German Expressionism, a cinematic movement of the 1910s and 1920s closely related to contemporaneous developments in theater, photography, painting, sculpture, and architecture. The opportunities offered by the booming Hollywood film industry and, later, the threat of growing Nazi power led to the emigration of many important film artists working in Germany who had either been directly involved in the Expressionist movement or studied with its practitioners. Directors such as Fritz Lang, Robert Siodmak, and Michael Curtiz brought dramatic lighting techniques and a psychologically expressive approach to mise-en-scène with them to Hollywood, where they would make some of the most famous of classic noirs. Lang's 1931 masterwork, the German M, is among the first major crime films of the sound era to join a characteristically noirish visual style with a noir-type plot, one in which the protagonist is a criminal (as are his most successful pursuers). M was also the occasion for the first star performance by Peter Lorre, who would go on to act in several formative American noirs of the classic era.