A true film noir would have some or many of these elements:

1. A morally ambiguous protagonist
2. A femme fatale, usually blonde
A central crime
High contrast black and white photography, deep shadows
5. Odd, jumbled framing
6. A voice-over narrative; story told in flashback (the plot is therefore inevitable)
7. A convoluted plot, unexpected turns
8. The men wear fedoras
9. Everyone smokes
10. A fatalistic or cynical philosophy ("The little guy can never win")
11. An urban setting, usually at night (the title sequence often features the city at night)
12. A sad ending, or a less than entirely happy ending
. Right-wing directors: a police procedural style of plot
14. Left-wing directors: pronounced social commentary
15. The past comes back to haunt the protagonist
16. A couple on the run from the police
Made between 1940-1960 (around 1948 was the peak)
18. A dreamlike mood
The protagonist is emotionally detached and cool
20. The bad guys are sadistic and/or psychotic
21. Desire and desperation are often present
22. Corrupt authority figures
23. Adapted from a book by Dashiell Hammett, Raymond Chandler, Mickey Spillane or James M. Cain