When studying the origins of such genres as horror and film noir (though it is debatable whether noir is actually a genre or a style / aesthetic), it is necessary to be aware of the influence of German Expressionism, a style of filmmaking developed during the Weimar years in Germany, particularly in 1920s Berlin.

World War 1 meant that Germany could no longer import films from France, Italy and America, forcing them to import from Scandinavia. These movies tended to emphasise cinematography above plot and narrative; often very slowly paced, for example, they were generally beautifully photographed, and this visual clarity had a pronounced effect on later German cinema. Danish cinema in particular was seen as being hugely influential, both in terms of style (lighting, scenic design and camera placement) and content (urban setting, focus on the criminal underworld and designed to deliver visceral thrills.) See, as an example, the works of Scandinavians Sjostrom and Stiller. It was particularly influential on the work of Fritz Lang. 

German Film, in common with that of other nations, started to become more of an 'art form' in the years after World War 1 but, although the film industry was booming, the Germans could not compete with huge American budgets. As such, directors like Lang and Murnau experimented instead with light and shadow (leading to the chiaroscuro style of lighting (essentially, very low-key lighting designed to emphasise extreme pockets of light and dark) which is possibly the key feature of film noir, and, as such, much neo-noir and, more generally, horror and crime genre film ever since.) In keeping with the shadowy aesthetic, themes tend to be dark (something of a tradition in German literature); crime, soulessness and, in general, the darker side of human nature are emphasised. The influence was driven forward when the Nazis took control of Germany and many of the directors, cinematographers and so on who had crafted this style fled to America.

The texts most commonly used as examples of German Expressionism (or heavily influenced by it) are those by Fritz Lang (Metropolis (1927) and M (1931), or F.W. Murnau's Nosferatu (1922.) Robert Wiene's The Cabinet of Dr Caligari (1920) is also hugely important.