I Know What You Did Last Summer is a 1997 American slasher film directed by Jim Gillespie and written by Kevin Williamson.

It stars Jennifer Love Hewitt, Sarah Michelle Gellar, Ryan Phillippe, and Freddie Prinze Jr., with supporting roles played by Johnny Galecki, Bridgette Wilson, Anne Heche, and Muse Watson.

The first installment in the I Know What You Did Last Summer franchise, it is loosely based on the 1973 novel by Lois Duncan.

The film centers on four teenage friends who are stalked by a hook-wielding killer one year after covering up a car accident in which they supposedly killed a man.

It also draws inspiration from the urban legend known as "the Hook", as well as the slasher films Prom Night (1980) and The House on Sorority Row (1982).