Once Upon a Time...in Hollywood is a 2019 comedy drama film written and directed by Quentin Tarantino. Produced by Columbia Pictures, Bona Film Group, Heyday Films, and Visiona Romantica and distributed by Sony Pictures, it is a co-production between the United States, United Kingdom, and China. It features a large ensemble cast led by Leonardo DiCaprio, Brad Pitt, and Margot Robbie. Set in 1969 Los Angeles, the film follows a fading actor and his stunt double as they navigate the rapidly changing film industry, with the threat of the Tate murders looming.

Announced in July 2017, it is the first Tarantino film not to involve Bob and Harvey Weinstein, as Tarantino ended his partnership with the brothers following the sexual abuse allegations against the latter. After a bidding war, the film was distributed by Sony Pictures, which met Tarantino's demands including final cut privilege. Pitt, DiCaprio, Robbie, Zoë Bell, Kurt Russell, and others joined the cast between January and June 2018. Principal photography lasted from June through November around Los Angeles. Once Upon a Time in Hollywood is the final film to feature Luke Perry, who died on March 4, 2019, and it is dedicated to his memory.

Once Upon a Time in Hollywood premiered at the 2019 Cannes Film Festival on May 21, 2019, and was theatrically released in the United States on July 26, 2019, and in the United Kingdom on August 14. It grossed $374 million worldwide and received acclaim from critics, with praise for Tarantino's direction and screenplay, the performances (particularly from DiCaprio and Pitt), cinematography, soundtrack, sound design, costume design, and production values. The National Board of Review and the American Film Institute named Once Upon a Time in Hollywood one of the top-ten films of 2019. Once Upon a Time in Hollywood was nominated for ten awards at the 92nd Academy Awards, winning two (Best Supporting Actor for Pitt and Best Production Design), and received numerous other accolades. A novelization, written by Tarantino in his debut as an author, was published in 2021.