Horizon: An American Saga – Chapter 1 is a 2024 American epic Western film directed and produced by Kevin Costner from a screenplay he co-wrote with Jon Baird, based on an original story by the pair and Mark Kasdan. The first installment in the titular film series, it features an ensemble cast of Costner, Sienna Miller, Sam Worthington, and Giovanni Ribisi, with Jena Malone, Abbey Lee, Michael Rooker, Danny Huston, Luke Wilson, Isabelle Fuhrman, Jeff Fahey, Will Patton, Tatanka Means, Owen Crow Shoe, Ella Hunt, and Jamie Campbell Bower in supporting roles. The film follows several characters navigating life in the Midwestern territories amid the American Civil War.

Costner conceived the idea for an epic Western film in 1988, but it languished in development hell for several decades. The film was finally confirmed in January 2022 with Costner as director, with an original plan to shoot the first two films of an envisioned four-film saga back-to-back and release them digitally on HBO Max. Much of the cast signed on in August, with filming beginning that month in Utah and lasting through November. The first two films carry a reported combined budget of $100 million, of which $38 million Costner personally funded.

Chapter 1 premiered at the 77th Cannes Film Festival on May 19, 2024, and was theatrically released in the United States on June 28, 2024. The film received mixed reviews from critics and grossed $38.7 million worldwide. The film was filmed back-to-back with a sequel, Chapter 2, which had its world premiere at the 81st Venice International Film Festival, and is scheduled to be released at an unspecified date in 2025; Chapter 3 started filming in May 2024, while Chapter 4 is in development.