Amy Adams said writer/director Spike Jonze would essentially lock her and Joaquin Phoenix in a room together for an hour or two every other day, and make them talk to each other. Jonze did this so that the actors could get to know each other better. Adams credits this for her and Phoenix's close friendship.
Samantha Morton was originally the voice of Samantha. She was present on the set with Joaquin Phoenix every day. After the filming wrapped and Spike Jonze started editing the movie, he felt like something was not right. With Morton's blessing, he decided to recast the role and Scarlett Johansson was brought and replaced Morton, re-recording all the dialogue.
Most of the city backgrounds, especially the ones featuring skyscrapers, are actually filmed in Shanghai. You can see many very identifiable skyscrapers such as the Shanghai World Financial Center. There are even Chinese signs if you look carefully.
Stuck in the editing process with his early 150-minute cut, Spike Jonze asked Steven Soderbergh to edit it down with his instincts. Soderbergh came back within 24 hours with a 90-minute cut, which helped Jonze make the final version which ran 126 minutes.
During some of the more emotional scenes, Amy Adams would sing songs from famous musicals like "Annie" and "The Rocky Horror Picture Show" in order to cheer herself up. Eventually, Joaquin Phoenix would join in and they would sing together. However, they stopped after they saw Spike Jonze filming them.
Spike Jonze said he met with the design team behind The High Line, an elevated park on Manhattan's West Side, to discuss the futuristic look of his Her (2013). He also revealed that he was inspired by the colors at Jamba Juice.
One legacy of Samantha Morton's casting is the name of Theodore's operating system. Both lead female roles take the same name as their lead actresses, Amy from actress Amy Adams and Samantha from Morton, but since she had to be re-cast at the last minute, the OS's name stayed Samantha.
Sofia Coppola won the 2003 Best Original Screenplay Oscar for "Lost in Translation," which was loosely inspired by her relationship with her then-husband Spike Jonze (played by Giovanni Ribisi in the film). Ten years later, Jonze would win the same award for "Her;" both films star Scarlett Johansson.
When Samantha is helping Theo at work with proof-reading of some letters she says ".. but I'm not much of a poet so I think I might have messed them up a bit". This may be a reference to an Alan Turing paper on Computing and Artificial Intelligence in which he proposes a possible test of a computer's intelligence by posing questions which the computer answers. He proposes the following question and answer as an example: Q: Please write me a sonnet on the subject of the Forth Bridge. A: Count me out on this one. I never could write poetry.
Woody Allen was a big influence on the film's script. "One of the movies I watched when I was writing Her (2013) was Crimes and Misdemeanors (1989) because that script is so incredibly written," Jonze explained. "There's a lot of talking about the idea of what the movie is about, but mostly the characters are plowing through the story, and taking you through the story, with their decisions. That was really inspiring."
When Spike Jonze wrote the first draft he didn't know the title of the movie and was about to FedEx it to a couple of people to read. He put "Untitled Rick Howard Project" on the cover. It then, "went out to [Spike's] agent, Warner Brothers and then from that point on for a year and a half every email, every contract was regarding 'Untitled Rick Howard Project' and no one knew who Rick Howard was". Rick Howard is one of four partners in Girl Skateboards with Spike Jonze. Spike has said he would drive up to the studio, the security guard would stop him and he would say "I'm with Rick Howard." The security guard would say, "You're with Rick Howard? OK go on."
The apartment scenes have all been filmed on location. In order to get the best lighting conditions possible Dutch cinematographer Hoyte van Hoytema decided to change all windows surrounding the apartment on the 34th floor. Additionally he decided to install large mirrors on the helicopter platform of the skyscraper across the street. This gave him the possibility to bounce back sunlight into the apartment.
Rooney Mara and Joaquin Phoenix have worked together in Her (2013), Mary Magdalene (2018) and Don't worry, He won't get far on foot (2018). They started dating during the production of Mary Magdalene in 2016.