The TSPDT 250 Quintessential Noir Films list contains 241 films that all contain three key ingredients.
1) They were all produced in the United States;
2) They were all shot in black-and-white;
3) They were all produced between 1940 to 1959.
The nine films that have been included that exclude at least one of these key ingredients are two non-American-produced noir (The Third Man and Mr. Arkadin), four color noir films (Leave Her to Heaven, Niagara, Party Girl and Slightly Scarlet), and three films from the early 1960s (Cape Fear, Underworld, U.S.A. and The Naked Kiss).