Iron Man (Robert Downey Jr.), Thor (Chris Hemsworth), the Hulk (Mark Ruffalo) and the rest of the Avengers face their most powerful enemy yet, the evil Thanos (Josh Brolin).
The heroes are joined by Spider-Man (Tom Holland) and Doctor Strange (Benedict Cumberbatch).
In a surprise twist revealed in the trailer, the heroes also team up with Peter Quill (Chris Pratt) and his Guardians of the Galaxy co-stars.
The film is a sequel to The Avengers (2012) and The Avengers: Age of Ultron (2015).
The story will spill over to a fourth, still-untitled Avengers movie which will mark the end of “phase three” of the Marvel cinematic universe (MCU),
20 films have already been planned for the fourth phase, though only two have so far been announced.
Infinity War is due in UK cinemas on 27 April 2018 and US cinemas a week later.