Phase Three of the Marvel Cinematic Universe (MCU) is a group of American superhero films produced by Marvel Studios based on characters that appear in publications by Marvel Comics. The MCU is the shared universe in which all of the films are set. The phase, which began with Captain America: Civil War in May 2016, features individual superhero films that build to the crossover films Avengers: Infinity War (2018) and Avengers: Endgame (2019). It includes two Spider-Man films that were co-productions between Marvel Studios and Columbia Pictures, including Spider-Man: Far From Home which ended Phase Three in July 2019. Phases One, Two, and Three make up "The Infinity Saga" storyline.

Kevin Feige produced every film in the phase, with Amy Pascal also producing Spider-Man: Homecoming (2017) and Far From Home, and Stephen Broussard also producing Ant-Man and the Wasp (2018). Civil War, Infinity War, and Endgame directors Anthony and Joe Russo and writers Christopher Markus and Stephen McFeely collaborated with the creative teams for each film in the phase. The films star Chris Evans as Steve Rogers / Captain America in Civil War, Benedict Cumberbatch as Dr. Stephen Strange in Doctor Strange (2016), Chris Pratt as Peter Quill / Star-Lord in Guardians of the Galaxy Vol. 2 (2017), Tom Holland as Peter Parker / Spider-Man in the Spider-Man films, Chris Hemsworth as Thor in Thor: Ragnarok (2017), Chadwick Boseman as T'Challa / Black Panther in Black Panther (2018), Paul Rudd as Scott Lang / Ant-Man and Evangeline Lilly as Hope van Dyne / Wasp in Ant-Man and the Wasp, and Brie Larson as Carol Danvers / Captain Marvel in Captain Marvel (2019); all returned for one or both of the crossover films. Evans and Holland have the most appearances in the phase, each starring or making cameo appearances in five films. Walt Disney Studios Motion Pictures distributed the films except for the Spider-Man films, which were released by Sony Pictures Releasing. The phase's films grossed over US$13.5 billion at the global box office and received generally positive critical and public responses. Endgame became the highest-grossing film at the time. The phase is seen as the franchise's best, with consistent quality and a cohesive overarching story.

Each feature film received tie-in comic books and some were marketed using the in-universe news shows WHIH Newsfront and The Daily Bugle. Marvel Studios also released the Team Thor mockumentary shorts series which expand on Thor's portrayal in Ragnarok. In 2024, a group of television series based on Marvel Comics that were produced by Marvel Television, separately from Marvel Studios, for the streaming service Netflix were retroactively added to the MCU timeline, primarily alongside Phase Three content.