The "I Know What You Did Last Summer" franchise is an American horror media franchise owned by Sony Pictures Entertainment. It consists of four slasher films and one television series, based on the 1973 novel by Lois Duncan. The franchise follows various characters who face a masked hook-wielding killer after they cover up a tragic accident they are involved in. The main entries in the franchise include:
- The original film "I Know What You Did Last Summer" (1997), which launched the franchise and became a teen horror classic.
- The theatrical sequel "I Still Know What You Did Last Summer" (1998).
- A direct-to-video standalone sequel titled "I'll Always Know What You Did Last Summer" (2006), with a new cast.
- A television series adaptation released by Amazon Prime Video in 2021.
- A legacy sequel released in 2025, reuniting actors from the original films.
The franchise is known for its mix of teen drama and slasher horror, iconic masked killer with a hook, and its cult following. Jennifer Love Hewitt and Freddie Prinze Jr. are prominent stars who reprise roles in multiple installments. The films have collectively grossed $274 million worldwide and have had mixed critical receptions, with the original film being the most celebrated. The story generally revolves around a group of friends who accidentally hit a man with their car, keep it a secret, and then are stalked by a killer who knows what they did last summer.