Its visual intricacy and complex, voiceover narrative structure are echoed in dozens of classic films noir.
Italian neorealism of the 1940s, with its emphasis on quasi-documentary authenticity, was an acknowledged influence on trends that emerged in American noir.
Edeson later photographed The Maltese Falcon (1941), widely regarded as the first major film noir of the classic era.
Josef von Sternberg was directing in Hollywood at the same time.
Films of his such as Shanghai Express (1932) and The Devil Is a Woman (1935), with their hothouse eroticism and baroque visual style, anticipated central elements of classic noir.
The commercial and critical success of Sternberg's silent Underworld (1927) was largely responsible for spurring a trend of Hollywood gangster films.
The Lost Weekend (1945), directed by Billy Wilder, another Vienna-born, Berlin-trained American auteur, tells the story of an alcoholic in a manner evocative of neorealism.
While noir is often associated with an urban setting, many classic noirs take place in small towns, suburbia, rural areas, or on the open road; setting, therefore, cannot be its genre determinant, as with the Western.
An 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.
The aesthetics of film noir are influenced by German Expressionism, an artistic movement of the 1910s and 1920s that involved theater, photography, painting, sculpture and architecture, as well as cinema.
The authors' caveats and repeated efforts at alternative definition have been echoed in subsequent scholarship: in the more than five decades since, there have been innumerable further attempts at definition, yet in the words of cinema historian Mark Bould, film noir remains an "elusive phenomenon […] always just out of reach".
Film analyst Eddie Muller writes, “If a private eye is hired by an old geezer to prove his wife’s cheating on him and the shamus discovers long-buried family secrets and solves a couple of murders before returning to his lonely office – that’s detective fiction.