In October 2003, 19-year-old Harvard University student Mark Zuckerberg is dumped by his girlfriend Erica Albright. Returning to his dorm, Zuckerberg writes an insulting entry about Albright on his LiveJournal blog and then creates a campus website called Facemash by hacking into college databases to steal photos of female students, then allowing site visitors to rate their attractiveness. After traffic to the site crashes parts of Harvard's computer network, Zuckerberg is given six months of academic probation. However, Facemash's popularity attracts the attention of Harvard upperclassmen and twins Cameron and Tyler Winklevoss and their business partner Divya Narendra. The trio invites Zuckerberg to work on Harvard Connection, a social network featuring the exclusive nature of Harvard students and aimed at dating.

After agreeing to work on the Winklevoss twins' concept, Zuckerberg approaches his friend Eduardo Saverin with an idea for what he calls Thefacebook, an online social networking website that would be exclusive to Ivy League students. Saverin provides $1,000 in seed funding, allowing Mark to build the website, which quickly becomes popular. When they learn of Thefacebook, the Winklevoss twins and Narendra are incensed, believing that Zuckerberg stole their idea while keeping them deliberately in the dark by stalling on developing the Harvard Connection website. They raise their complaint with Harvard President Larry Summers, who is dismissive and sees no value in either disciplinary action or Thefacebook website itself.

Saverin and Zuckerberg meet fellow student Christy Lee, who asks them to "Facebook me", a phrase which impresses both of them. As Thefacebook grows in popularity, Zuckerberg extends the network to Yale University, Columbia University and Stanford University. Lee arranges for Saverin and Zuckerberg to meet Napster co-founder Sean Parker, who presents a "billion dollar" vision for the company that impresses Zuckerberg. He also suggests dropping "The" from Thefacebook, just calling it Facebook. At Parker's suggestion, the company moves to Palo Alto, with Saverin remaining in New York to work on business development. After Parker promises to expand Facebook to two continents, Zuckerberg invites him to live at the house he is using as company headquarters.

While competing in the Henley Royal Regatta for Harvard against the Hollandia Roeiclub, the Winklevoss twins discover that Facebook has expanded to Oxford, Cambridge and LSE, and decide to sue the company for theft of intellectual property. Meanwhile, Saverin objects to Parker making business decisions for Facebook and freezes the company's bank account in the resulting dispute. He later relents when Zuckerberg reveals that they have secured $500,000 from angel investor Peter Thiel. However, Saverin becomes enraged when he discovers that the new investment deal allows his share of Facebook to be diluted from 34% to 0.03%, while maintaining the ownership percentage of all other parties. He confronts Zuckerberg and Parker, and Saverin vows to sue Zuckerberg for all the company's shares before being ejected from the building. Subsequently, Saverin's name is removed from the masthead as co-founder. Later, a cocaine possession incident involving Parker and his attempt to place the blame on Saverin finally convinces Zuckerberg to cut ties with him.

Throughout the film, the narrative is intercut with scenes from depositions taken in the Winklevoss twins' and Saverin's respective lawsuits against Zuckerberg and Facebook. The Winklevoss twins claim that Zuckerberg stole their idea, while Saverin claims his shares of Facebook were unfairly diluted when the company was incorporated. At the end, Marylin Delpy, a junior lawyer for the defense, informs Zuckerberg that they will settle with Saverin, since the sordid details of Facebook's founding and Zuckerberg's own callous attitude will make him highly unsympathetic to a jury. After everyone leaves, Zuckerberg is shown sending a friend request to Albright on Facebook and then refreshing the webpage every few seconds as he waits for her response.

The epilogue states that Cameron and Tyler Winklevoss received a settlement of $65 million, signed a non-disclosure agreement, and rowed in the 2008 Beijing Olympics, placing sixth; Eduardo Saverin received a settlement of an unknown amount and his name was restored to the Facebook masthead as a co-founder; the website has over 500 million members in 207 countries and is valued at $25 billion; and Mark Zuckerberg is the world's youngest self-made billionaire.

Screenplay

Screenwriter Aaron Sorkin said, "What attracted me to had nothing to do with Facebook. The invention itself is as modern as it gets, but the story is as old as storytelling; the themes of friendship, loyalty, jealousy, class and power. I got a 14-page book proposal that Ben Mezrich had written for his publisher for a book he was going to call The Accidental Billionaires. The publisher was simultaneously shopping it around for a film sale. That's how it wound up in my hands. I was reading it and somewhere on page three I said yes. It was the fastest I said yes to anything. But Ben hadn't written the book yet, and I assumed that Sony was going to want me to wait for Ben to write the book, and I would start a year from now. They wanted me to start right away. Ben and I were kind of doing our research at the same time, sort of along parallel lines."

However, according to Sorkin, Mezrich did not send him material from his book as he wrote it: "Two or three times we'd get together. I'd go to Boston, or we'd meet in New York and kind of compare notes and share information, but I didn't see the book until he was done with it. By the time I saw the book, I was probably 80 percent done with the screenplay." Sorkin elaborated:

Casting

Casting began in early August 2009, with open auditions held in various states. Jesse Eisenberg was first announced to be attached to the project in September 2009. (Coincidentally, in an interview with Diane Sawyer on ABC's World News with Diane Sawyer, Zuckerberg revealed that Eisenberg's cousin, Eric Fisher, was a Facebook product designer.) Several days later, Justin Timberlake and Andrew Garfield were confirmed to portray the roles of Sean Parker and Eduardo Saverin, respectively. In October 2009, Brenda Song, Rooney Mara, Armie Hammer, Shelby Young, and Josh Pence were cast. Max Minghella and Dakota Johnson were also confirmed to star in the film. In a 2009 interview with The Baltimore Sun, Eisenberg said, "Even though I've gotten to be in some wonderful movies, this character seems so much more overtly insensitive in so many ways that seem more real to me in the best way. I don't often get cast as insensitive people, so it feels very comfortable: fresh and exciting, as if you never have to worry about the audience. Not that I worry about the audience anyway – it should be just the furthest thing from your mind. The Social Network is the biggest relief I've ever had in a movie".

Filming

Principal photography began in October 2009 in Cambridge, Massachusetts. Scenes were filmed around the campuses of two Massachusetts prep schools, Phillips Academy and Milton Academy. Additional scenes were filmed on the campus of Wheelock College, which was set up to be Harvard's campus. (Harvard has turned down most requests for on-location filming ever since the filming of Love Story (1970), which caused significant physical damage to the campus.) Filming took place on the Keyser and Wyman quadrangles in the Homewood campus of Johns Hopkins University from November 2–4, which also doubled for Harvard in the film. The first scene in the film, where Zuckerberg is with his girlfriend, took 99 takes to finish. The film was shot on the Red One digital cinema camera. The rowing scenes with the Winklevoss brothers were filmed at Community Rowing Inc. in Newton, Massachusetts and at the Henley Royal Regatta. Although a significant portion of the latter half of the film is set in Silicon Valley, the filmmakers opted to shoot those scenes in Los Angeles and Pasadena. Miniature faking process was used in a sequence showing a rowing event at the Henley Royal Regatta.

Armie Hammer, who portrayed the Winklevoss twins, acted alongside body double Josh Pence while his scenes were filmed. His face was later digitally grafted onto Pence's face during post-production, while other scenes used split-screen photography. Pence was concerned about having no face time during the role, but after consideration thought of the role as a "no-brainer". He also appears in a cameo role elsewhere in the film. Ham