Let the Right One In (Swedish: Låt den rätte komma in) is a 2008 Swedish romantic horror film directed by Tomas Alfredson and written by John Ajvide Lindqvist, who adapted his 2004 novel. The film tells the story of a bullied 12-year-old boy who develops a friendship with a strange child in Blackeberg, a suburb of Stockholm, in the early 1980s.

A film adaptation of Lindqvist's novel began development in 2004 when John Nordling acquired the rights to produce the project. Alfredson, unconcerned with the horror and vampire conventions, decided to tone down many elements of the novel and focus primarily on the relationship between the two main characters and explore the darker side of humanity. Selecting the lead actors involved a year-long process with open castings held all over Sweden. In the end, Kåre Hedebrant and Lina Leandersson were chosen for the leading roles. Leandersson's role in the film was dubbed by Elif Caylan. Principal photography took place in 2007 in Luleå, with additional filming in Blackeberg. The film was produced by EFTI, Sveriges Television and Filmpool Nord, with support from the Swedish Film Institute, Nordisk Film & TV Fond, WAG and Canal+.

Let the Right One In premiered at the Gothenburg Film Festival on 26 January 2008, where it received the Nordic Film Prize. It was released in Sweden on 24 October 2008 by Sandrew Metronome. The film received critical acclaim, with praise for the performances of the two leads, the cinematography, screenplay, and direction. It won several awards, including the Founders Award for Best Narrative Feature at the Tribeca Film Festival, as well as four Guldbagge Awards, including Best Director for Alfredson, Best Cinematography for Van Hoytema, and Best Screenplay for Lindqvist. It also won the Saturn Award for Best International Film and the Empire Award for Best Horror Film. At the 63rd British Academy Film Awards, the film was nominated for Best Film Not in the English Language. An American remake, titled Let Me In, was released in 2010.

Oskar resides with his mother in the Swedish suburb of Blackeberg in 1982. His classmates bully him, and he spends his evenings imagining revenge. One evening, he meets Eli, who appears to be a girl his age. Eli has moved into the adjoining apartment with a man, Håkan. Eli informs Oskar they cannot be friends, but the two begin exchanging coded messages through their shared wall. Eli learns Oskar is being bullied by schoolmates and encourages him to stand up for himself. Oskar then enrolls in exercise classes after school.

Håkan kills a person on a footpath to harvest blood for Eli, but is interrupted by a passerby. Eli is prompted to waylay and kill a man, Jocke. A recluse witnesses the attack from his flat but doesn't report the incident. Håkan hides Jocke's body in a hole in the lake. Håkan makes another effort to obtain blood for Eli by trapping a boy in a room after school. When he is unsuccessful, Håkan pours acid onto his own face to avoid identification. Eli visits Håkan in the hospital, where he offers his own neck for feeding. Eli drains him of his blood, and Håkan falls out the window. Eli goes to Oskar's apartment and spends the night with him, during which they agree to "go steady", though Eli states, "I'm not a girl".

While on a field trip, the bullies again harass Oskar, who this time hits their leader in the head with a pole, injuring him. On that same trip, some of Oskar's classmates discover Jocke's body. Oskar suggests he and Eli should form a bond and cuts his hand. Eli laps up his blood then runs away. Jocke's friend Lacke has a fight with his girlfriend Virginia, and afterward Eli attacks her. She survives but discovers that exposure to sunlight burns her skin. While in the hospital, she asks an orderly to open the blinds in her room, and bursts into flames, committing suicide.

Eli comes to Oskar's apartment and asks to be invited in, but he refuses. Eli then steps inside and starts to bleed profusely, which causes Oskar to relent. Eli admits to being a vampire who must drink human blood to survive, also insisting they both are alike in that Oskar wants to kill and Eli needs to kill, and encourages him to "be me, for a little while." Later when Eli changes clothes, Oskar is shocked to see a horizontal scar across Eli's pubic area with no genitals. (In the novel, Eli is an androgynous boy born as Elias, castrated by a vampire-nobleman)

Lacke sets out to kill Eli, whom he finds asleep in the apartment's bathtub. Oskar intervenes, and Eli wakes up and feeds on Lacke's blood. Afterward, Eli thanks Oskar and kisses him. Fearing they've attracted too much attention from the neighbors, Eli decides it isn't safe to stay and leaves that night. Oskar is lured out to resume the program at the pool. One of the bullies holds Oskar under the water. Eli arrives and rescues him by killing and dismembering the bullies, except for one, who is left sobbing on a bench.