"Now, where was I?"
Lenny has a problem. During a robbery in which his wife is killed, he suffers a blow to the head which gives him anterograde amnesia: His brain is unable to record new memories. He can remember the last five to fifteen minutes, and he can remember his life from before the injury, but everything in between is gone. Now his only goal is to track down his wife's killer.
To find John G, and to simply function from day to day, Lenny employs a variety of reminders and notes to himself, like Polaroids and tattoos. Of course, this isn't a perfect world, and in the hunt for John G, he comes across some who would take advantage of his condition...
The scenes in the movie are shown in backwards chronological order (alternating with normal chronological scenes of Lenny in the hotel room, shown in black-and-white), to create a mood matching Leonard's condition.
- Absence of Evidence: Leonard destroyed several documents, before the beginning of the film, which indicated that his wife's attacker had already been found and brought to justice. Furthermore, after Teddy shows him the photo he took of Leonard once the deed was done, he burns both it, AND the new photo he just took of the killed "John G.", to continue to delude himself into thinking his wife's killer was still at large.
- All There in the Manual: Much of the backstory is only explained through the movie's promotional website, including Leonard sending himself messages to convince himself that there was a second burglar who murdered his wife, prompting his eventual escape from the institution he was in.
- Back to Front: The majority of the film is shown in reverse order. These scenes alternate with shorter scenes arranged chronologically. The two plot threads meet at the end of the film (which is the chronological middle of the story).
- Best Served Cold: Lenny's only motivation is to kill the man who murdered his wife. Assuming she was even murdered by the man, and not killed by Leonard giving her too many insulin injections.
- The Big Board
- Burn, Baby, Burn: Lenny disposes of several of his late wife's belongings this way.
- Country Matters: That's how Natalie finally gets Leonard to snap and punch her.
- Deliberately Monochrome: One thread of the movie is monochrome and the other is in color. The trope is played with very well when the plot threads' meeting point coincides with a developing Polaroid photo.
- Downer "Ending": At the end of the movie, you discover that Leonard is basically a Serial Killer, even if he doesn't remember any of his previous kills. Which is sad. But it's even sadder when you realize that at the end (which is the beginning of the movie) he killed the only person who had him in check. And because he doesn't remember a thing, he will continue to seek revenge, killing we don't know how many people in the process. Revenge for nothing, of course, since his wife didn't die in the attack at all, but was accidentally killed by Leonard, in the way he believes Sammy's wife died. Damn.
- Dynamic Entry: Subverted in one of the only funny moments in the movie.
- Easter Egg: The DVD is full of them, one that even lets you watch the film in chronological order.
- Film Noir
- Foregone Conclusion: "Teddy", AKA "John G"
is going to has beengets shot.
- Freeze-Frame Bonus: while Lenny is narrating the story of Sammy Jankis, a shot of Sammy sitting in a nursing home briefly changes to a shot of Lenny in the exact same spot and clothing
- It's All Junk: Lenny tosses several of his wife's belongings into a fire.
- Laser-Guided Amnesia: AVERTED!!! In fact, one of the few films that treats amnesia anywhere near realistically.
- Living Lie Detector: Leonard learned to do this before his injury as an insurance claims investigator. As such, it is extremely difficult to deceive him in a face to face conversation. Or so he believes.
- Note to Self: / Memory Gambit: Pretty much Leonard's only way of functioning from day to day.
- Ontological Mystery
- Platonic Prostitution
- The Usual Suspects Ending
- Unreliable Narrator
- What Did I Do Last Night?
- Xanatos Sucker: Natalie and Teddy just love using the protagonist's short-term memory in order to manipulate him and at the end, or rather, the middle, we learn that he actually manipulated "himself" into shooting Teddy by leaving indications that he was John G.