Zack Snyder's Justice League is the 2021 director's cut and the original version of the 2017 American epic superhero film Justice League, the fifth film set within the DC Extended Universe (DCEU), which is based on the team of the same name appearing in DC Comics. It is director Zack Snyder's original vision of the film prior to his departure from the production. The film follows Batman (Ben Affleck), Wonder Woman (Gal Gadot), Cyborg (Ray Fisher), Aquaman (Jason Momoa), the Flash (Ezra Miller), and Superman (Henry Cavill) as they form an alliance to stop the extradimensional New God Steppenwolf (Ciarán Hinds) and his army of Parademons from conquering Earth for his overlord, Darkseid (Ray Porter).

The production of the theatrical film was difficult, and the script frequently underwent major changes. In May 2017, Snyder stepped down during post-production following the death of his daughter, and Joss Whedon was hired to finish the film, completing it as an uncredited additional director. Whedon wrote and directed new sequences and incorporated a brighter, more humorous tone while significantly reducing the runtime in accordance with directives from Warner Bros. Pictures. The theatrical version polarized critics and underperformed at the box office, resulting in Warner Bros. developing future DCEU films around individual characters with less emphasis on a wider shared universe.

Many people expressed interest in Snyder's version of the film, often colloquially referred to as the Snyder Cut. Although most industry insiders reported its release unlikely, Warner Bros. moved ahead with it in February 2020. In May 2020, Snyder announced it would be released as Zack Snyder's Justice League on HBO Max. $70 million was spent to complete the visual effects, score, and editing, with new material being shot in October 2020. The film is dedicated to the memory of Autumn Snyder. Zack Snyder's Justice League was released on HBO Max in the United States on March 18, 2021. It became the fourth-most-streamed film on the platform that year. The film was released to positive reviews from critics, who generally considered it better than the theatrical cut, but criticized the lengthy runtime.