Paranormal Activity 2 is a 2010 American found footage supernatural horror film directed by Tod Williams, and written by Michael R. Perry, Christopher Landon and Tom Pabst. It is the second installment of the Paranormal Activity film series. The film mostly acts as a prequel to the 2007 film Paranormal Activity, beginning two months before the events depicted in the original film, although it is set over a longer period of time and eventually concludes after the first film's ending.

The film stars Sprague Grayden, Brian Boland, Molly Ephraim, Seth Ginsberg, Micah Sloat and Katie Featherston, the latter two reprising their roles as Micah and Katie from the first film. The film follows the family of Katie's sister Kristi, who start suspecting that a supernatural entity is tormenting them.

Paranormal Activity 2 was released in theaters at midnight on October 22, 2010, in the United States, the United Kingdom, Canada, Mexico, Brazil, Argentina, Poland and Ireland. It received mixed reviews from critics and was a box-office success, grossing over $177 million against a $3 million budget. An unrated version of the film was also released.

In August 2006, a "burglary" occurs at the home of Kristi and Daniel Rey, trashing their house and leaving only their infant son Hunter's bedroom untouched. The only thing stolen is a necklace that Kristi's sister, Katie, gave to her. Despite this, the family contact a home security company and have them install security cameras around the house. Martine, the Latin American family housekeeper and nanny, senses "evil spirits" in the house and burns sage to rid the house of them, and Daniel fires her for doing so. Kristi also believes that their home is haunted, and she and Katie talk about being tormented by a demon when they were children. Daniel, however, initially dismisses her claim despite footage of strange occurrences around the house. Daniel's daughter from a prior marriage, Ali, begins investigating the mysterious happenings; she discovers that humans can make deals with demons for wealth or power by forfeiting the soul of their first-born son, but if the deal is not fulfilled, the demon will stick to the family until another son is born — Hunter was the first male to be born on Kristi's side since the 1930s.

The violence escalates, as the family's German Shepherd, Abby, is attacked by the demon and apparently suffers from a seizure. As Daniel and Ali take Abby to the veterinarian, Kristi is attacked and dragged into the basement by the demon, who possesses her. The following day, Ali is left home with Kristi, unaware she is possessed. Soon, Ali hears a scratching sound from the basement door and opens it to find scratches and sees a word, meus (Latin for "Mine"), etched into it. A strange bite mark on her leg and the footage of Kristi's attack motivates Daniel to contact Martine for assistance, and she prepares a cross to exorcise the demon; Kristi will have no memory of having been possessed. Daniel plans to pass the demon onto Katie so that Kristi and Hunter will be saved, despite Ali's protests.

That night, when Daniel tries to use the cross on Kristi, she attacks him and the house lights all go out. Using the handheld camera's night vision, he walks around the shaking house into the basement, where he is attacked by Kristi; he retaliates against her with the cross, causing her to collapse and the house to shake violently before settling down. Daniel puts Kristi to bed and with Martine, burns a photo of a young Katie, passing the demon onto her. Three weeks later, Katie visits and explains that strange things have begun happening at her house. On October 9, the night after Micah is killed, a possessed and bloodstained Katie breaks into the Rey house, kills Daniel and Kristi and then takes Hunter with her. A title card explains that Ali comes home from a school trip to find their bodies, and Katie and Hunter have vanished.

Coming after the box office success of Paranormal Activity, distributor Paramount Pictures quickly pursued a sequel. Kevin Greutert, director of Saw VI, was slated to direct while Michael R. Perry was set to write the film in January 2010. Oren Peli, the writer and director of the first film, was not expected to be directly involved with the sequel, but approved of Perry's story. Days after his hiring, Greutert was suddenly pulled from the project after Twisted Pictures and Lionsgate used a clause in Greutert's contract to direct Saw 3D; only two weeks away from filming. Peli, who remained on board as a producer, was ruled out as a viable replacement due to his obligations to Area 51. Brian De Palma and Akiva Goldsman were early candidates for the directors chair. Goldsman instead became involved as an executive producer and would help shape the story, while De Palma met with Perry and Jason Blum. Circumstances changed and De Palma moved on, leading to Paramount looking toward Brad Anderson and Greg McLean. By March 2010, Katie Featherston and Micah Sloat were expected to reprise their roles. By the end of the month, Tod Williams was tapped to direct the film with production set to begin that May.

Production on Paranormal Activity 2 began without a completed script. Three weeks into filming, the footage was said to be "disastrous"; leading to a writer's room being assembled and production shutting down. Christopher Landon, one of the writers brought in, gave notes on the footage which prompted a studio executive to hire Landon and another unnamed writer to write half of the film. The pair's screenplay failed to satisfy the studio, and one final attempt by Landon alone was enough to reinvigorate the production.