Throughout the last 80 years, scholars and film critics have tried to define film noir and come up with various theories. Some claim film noir is a genre, others classify it as a style. The definition of the phenomenon appears to be rather elusive. In consequence, some films are classified as noir or neo-noir even though they seem not to meet the necessary requirements to be categorized as such. The following article examines the most popular theories on film noir and explains why it is impossible to construct one and final definition.