In October 2014, Marvel announced a two-part sequel to Avengers: Age of Ultron, titled Avengers: Infinity War. Part 1 was scheduled to be released on May 4, 2018, with Part 2 scheduled for May 3, 2019. In April 2015, Marvel announced that Anthony and Joe Russo would direct both films, with back-to-back filming expected to begin in 2016. The same month, Kevin Feige said the films would be two, distinct films "because they [have] such shared elements, it felt appropriate... to [subtitle the films] like that. But I wouldn’t call it one story that's cut in half. I would say it's going to be two distinct movies." In addition, according to Feige, the Avengers are expected to have a "shakeup" in their team lineup between Avengers: Infinity War and the untitled Avengers sequel. By May 2015, Christopher Markus and Stephen McFeely had signed on to write the screenplays for both parts of the film, which draws inspiration from Jim Starlin's 1991 The Infinity Gauntlet comic and Jonathan Hickman's 2013 Infinity comic. In a NY Times interview, when asked about how the script was written to accommodate the large cast, McFeely said, "Not every scene can be 25 people in a room. You're going to have to make kickball teams and then have a tournament." Anthony Russo added the film was inspired by 1990s heist films, with Thanos "on a smash-and-grab [to acquire the Infinity Stones], and everybody’s trying to catch up the whole movie." In May 2016, the Russos revealed that they would retitle the two films, to further remove the misconception that they were one large film split in two, with Joe Russo stating, "The intention is we will change [the titles], we just haven’t come up with [them] yet." That July, Marvel revealed the film's title would be shortened to simply Avengers: Infinity War. Between April 2016 to January 2017, many actors from previous MCU films were confirmed to be reprising their roles in the films.
In late January 2017, Principal photography began, under the working title Mary Lou, at Pinewood Atlanta Studios in Fayette County, Georgia as well as Downtown Atlanta. Additional locations included Edinburgh, Glasgow, Cumbernauld and the Scottish Highlands in Scotland, Durham, England, Queens, New York, and Ifugao, Philippines. IMAX stated that this film, along with the sequel, was entirely filmed with digital 2-D ARRI Alexa IMAX cameras, which are specially customized versions of ARRI Alexa 65 cameras with IMAX technology. Captain America: Civil War (2016) was the first Marvel Cinematic Universe film to incorporate the new cameras, but only for its airport sequence. This made Avengers: Infinity War the first non-documentary film to be shot entirely with IMAX cameras, although it did not use the traditional IMAX aspect ratio of 1.43:1 but rather the digital IMAX ratio of 1.90:1, which closely matches the 1.85:1 aspect ratio of The Avengers (2012) and Ant-Man (2015). In Early March 2018, Disney moved the release date to April 27 2018, releasing five days before the tenth anniversary of Iron Man (2008), to match the date in several international markets. In June 2016, Alan Silvestri, who composed the score for The Avengers, was revealed to be returning to score both Infinity War and its sequel. The visual effects for the film were created with the combined talents of Industrial Light & Magic, Framestore, Method Studios, Weta Digital, Double Negative, Cinesite, Digital Domain, Rise, Lola VFX, and Perception. With a running time of 156 minutes, this will make the film the longest Marvel film to date following Captain America: Civil War, which had a running time of 147 minutes. With an estimated budget between $300–400 million, the film would go on to become one of the most expensive films ever made.
The film features an ensemble cast that includes Robert Downey Jr., Chris Hemsworth, Mark Ruffalo, Chris Evans, Scarlett Johansson, Benedict Cumberbatch, Don Cheadle, Tom Holland, Chadwick Boseman, Paul Bettany, Elizabeth Olsen, Anthony Mackie, Sebastian Stan, Tom Hiddleston, Idris Elba, Benedict Wong, Pom Klementieff, Karen Gillan, Dave Bautista, Zoe Saldana, Vin Diesel, Bradley Cooper, Gwyneth Paltrow, Benicio del Toro, Chris Pratt, Danai Gurira, Letitia Wright, William Hurt, Winston Duke, Peter Dinklage, Terry Notary, Tom Vaughan-Lawlor, Carrie Coon, Michael James Shaw, and Josh Brolin. The cast gave spectacular performances that took their characters to whole other levels that we did not expect from the very first moment to the last.