What If...? is an American animated anthology series created by A. C. Bradley for the streaming service Disney+ based on the Marvel Comics series of the same name. It is the fourth television series in the Marvel Cinematic Universe (MCU) produced by Marvel Studios, and the studio's first animated series from Marvel Studios Animation. The series explores alternate timelines in the multiverse that show what would happen if major moments from the MCU films occurred differently. Bradley serves as head writer for the first two seasons, with Matthew Chauncey for the third, and Bryan Andrews as the lead director.

Jeffrey Wright stars as the Watcher, who narrates the series, alongside many MCU film actors reprising their roles. Marvel Studios was developing the series for Disney+ by the end of 2018, with Bradley and Andrews on board. It was officially announced in April 2019. Marvel Studios' head of visual development Ryan Meinerding helped define the series' cel-shaded animation style, which was designed to reflect the films and take inspiration from classic American illustrators. Animation for the series was provided by Flying Bark Productions and Stellar Creative Lab, with Blue Spirit and Squeeze also providing animation in the first season and SDFX Studios also animating in the second season. Stephan Franck served as head of animation in the first season, as well as a director on the second season, with Scott Wright as head of animation in the second. Chauncey, who served as the series' story editor, replaced Bradley as head writer for the third season.

The first season of What If...? premiered on August 11, 2021, and ran for nine episodes until October 6, as part of Phase Four of the MCU. The second season premiered on December 22, 2023, as part of Phase Five, and released its nine episodes daily until December 30. The series has received generally positive reviews, with praise for the voice acting, animation, creative storylines, and scenarios, although the episodes' length and writing received some criticism. A third season and a spin-off series titled Marvel Zombies are in development.