I love the psychological thriller genre, but I've always wondered what actually defines it. Two definitions come to mind: 1. A thriller that focuses on the psychological dimensions of the characters 2. A thriller in which the protagonist/s and antagonist/s engage in a battle not just on a physical level, but on a mental one as well. Some psycho-thrillers mix in elements from different genres, or otherwise subvert/avoid our expectations. Alfred Hitchcock's Psycho counts not only as a thriller, but as a slasher film, as do many works by Dario Argento. Marathon Man takes the story of a haunted grad student running from his past and applies it to a high-tension story of espionage and diamonds. The 2010 Edge of Darkness film does a similar thing, juxtaposing the conspiracy mystery with Mel Gibson's grief. Fight Club can be described as a psychological thriller, but the "thriller" part doesn't come until the last half-hour or so. If anything, its more of a dark dramedy. Psychological elements even pop up in different genres: the action/crime thriller Heat gives us a lot of insight into the characters of Al Pacino and Robert De Niro. In To Live and Die in L.A., a LOT of time is spent elaborating on how disturbingly similar William Petersen and Willem Defoe are, to the point that it could be considered a study of two self-destructive individuals.