Zack Snyder's Justice League (colloquially referred to as the Snyder Cut) is the 2021 director's cut of the 2017 American superhero film Justice League, the fifth film set within the DC Extended Universe (DCEU) based on the team of the same name appearing in DC publications and the follow-up to Batman v Superman: Dawn of Justice (2016). It is intended to match director Zack Snyder's original vision for the film, prior to his departure from the production and subsequent studio interference. 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).

Released by Warner Bros. Pictures in 2017, Justice League had a difficult production. Its script underwent major changes before and during production between 2016 and 2017. In May 2017, Snyder stepped down during post-production following the death of his daughter, Autumn Snyder, and Joss Whedon was hired to finish the film, completing it as an uncredited director. Whedon wrote and directed new sequences and oversaw reshoots and other changes that incorporated a brighter tone and more humor while reducing the runtime significantly in accordance with a mandate from Warner Bros. The theatrical version polarized critics and underperformed at the box office; this resulted in WB opting to prioritize developing future films around individual characters, with less regard for consistency and continuity within the wider shared universe.

Many people expressed interest in Snyder's version of the film, often referred to as the "Snyder Cut." Although most industry insiders reported its release unlikely, WB moved ahead with it in February 2020; in May, Snyder announced it would be released as Zack Snyder's Justice League as an HBO Max Original Film. $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. Critics generally considered the film an improvement over the 2017 theatrical release.