Classic NoirThere are a lot of debates about what makes a film noir, and whether in fact it is a genre unto itself, or simply a style. My own sense of it is that noir began as a particular genre, growing out of interwar German expressionist filmmaking (M is often named as the originator of the genre), but evolved into a "style," that is a set of "noirish" elements -- including character types (grifters and conmen, cynical cops, private eyes, femmes fatales); stylistic points (urban nightscapes, rain or fetid heat, rotating fans, voice-overs); plot elements (heists gone wrong, adultery, double-crosses); settings and locations (from anonymous small towns and seedy hotels to Los Angeles and Central European cities) -- that can be introduced or remixed into any other genre. Thus it is possible to have "Sci-fi noir" (e.g. Blade Runner), "Western noir" (e.g., 3:10 to Yuma), "Comedy noir" (e.g. Fargo), "Horror noir" (e.g., The Brute Man), and so on.
Ultimately, what makes a film noir is less any of the above elements than a certain sensibility of what one might call alienated fatalism: a sense that the world as a whole is ultimately defined by corruption in every sense of that word (moral, financial, physical). Some critics have naturally chosen to label that attitude as a "cynical" but I would reject that; as always, the word "cynical" is just a scare word that foolish optimists use to malign realists. With that said, I should admit that my interest in deviant globalization is closely related to my predilection for film noir.