Divya Narendra, Cameron Winklevoss, and Tyler Winklevoss, founders of the social network ConnectU, filed a lawsuit against Facebook in September 2004. The lawsuit alleged that Zuckerberg had broken an oral contract to build the social-networking site, copied the idea,^[1][2] and used source code that they provided to Zuckerberg to create competing site Facebook.^[3][4][5][6] Facebook countersued in regards to Social Butterfly, a project put out by The Winklevoss Chang Group, an alleged partnership between ConnectU and i2hub. It named among the defendants ConnectU, Cameron Winklevoss, Tyler Winklevoss, Divya Narendra, and Wayne Chang, founder of i2hub.^[7] The parties reached a settlement agreement in February 2008, for $20 million in cash and 1,253,326 Facebook shares. On August 26, 2010, The New York Times reported that Facebook shares were trading at $76 per share in the secondary market, putting the total settlement value now at close to $120 million.^[8][9]

ConnectU filed another lawsuit against Facebook on March 11, 2008,^[10] attempting to rescind the settlement, claiming that Facebook, in settlement negotiations, had overstated the value of stock it was granting the ConnectU founders as part of the settlement. ConnectU argued that Facebook represented itself as being worth $15 billion at the time, due to the post-money valuation arising from Microsoft's purchase in 2007 of a 1.6% stake in Facebook for US$246 million. Facebook announced that valuation in a press release.^[11] However, Facebook subsequently performed an internal valuation that estimated a company value of $3.75 billion.^[12] ConnectU then fired the law firm Quinn Emanuel that had represented it in settlement discussions. Quinn Emanuel filed a $13 million lien against the settlement proceeds and ConnectU sued for malpractice.^[13] On August 25, 2010, an arbitration panel ruled that Quinn Emanuel had "earned its full contingency fee". It also found that Quinn Emanuel committed no malpractice.^[14] ConnectU's lawsuit against Facebook to quadruple its settlement remains ongoing.

In January 2010, it was reported that i2hub founder Wayne Chang and The i2hub Organization launched a lawsuit against ConnectU and its founders, Cameron Winklevoss, Tyler Winklevoss, and Divya Narendra, seeking 50% of the settlement. The complaint states "Through this litigation, Chang asserts his ownership interest in The Winklevoss Chang Group and ConnectU, including the settlement proceeds."^[15] Lee Gesmer (of Gesmer Updegrove, LLP) posted the detailed 33-page complaint online.^[16][17] On April 12, 2011, a three-judge panel of a federal appeals court in San Francisco ruled that the Winklevoss brothers, whose fight over Facebook's origins was a major narrative arc of the film The Social Network, cannot back out of a settlement they signed with the company in 2008.

Seven months after the initial launch of houseSYSTEM Greenspan added a new social networking module called FaceNet to compete with Facebook, telling the Harvard Crimson, "It is possible for multiple sites to co-exist. [We support] entrepreneurship, and we applaud Mark’s efforts. Competition is a very real part of entrepreneurship".^[20] However, students who had tried both websites expressed doubts about Greenspan's website noting that "FaceNet isn’t as easy to use as thefacebook.com. It might be too little, too late. It will be hard to compete with thefacebook.com when thefacebook.com already has about 5,000 members and lots of momentum".^[20]

In 2006, two years after Mark Zuckerberg launched thefacebook.com, Greenspan claimed in an open letter to Zuckerberg that Facebook used features that originally belonged to houseSYSTEM.^[21] Regarding Greenspan's allegations, years later Zuckerberg was described in The New York Times as "saying through a spokeswoman that he was not sure how to respond".^[22] Greenspan later filed a Petition to Cancel the "Facebook" trademark at USPTO.^[23] Facebook, Inc. agreed to a formal settlement with Greenspan in late May 2009 and issued a press release, but the terms were not disclosed.^[24]

On 15 February 2022, Racine's lawyers stated that Facebook had not arranged Zuckerberg's deposition, despite a court judge allowing it in a January 10 order. On February 1, Facebook's lawyers requested the judge to block Zuckerberg's deposition, arguing that he does not have any information to give and that the District's efforts were an attempt at harassment. A filing by the District urged the judge to allow the deposition to proceed,^[72] which was later denied by the judge, calling the attempt "frankly annoying."^[73]

In February 2020, the Internal Revenue Service sued Facebook for tax evasion, claiming that they had sheltered $9 billion from taxes in Ireland due to its low corporate tax rates, the central point of the case being that Facebook settled a deal with an Irish subsidiary in 2010 that allows them to shuffle money around internationally.^[84]

The lawsuit was initially dismissed in June 2021 but was launched again in an amended state in August 2021, citing Facebook's buyouts of rivals as a cause for alarm. In March 2022, the Chamber of Commerce rejected the 46 states' appeal to revive their lawsuit, citing the overly long waiting period between Facebooks's acquisition of WhatsApp and Instagram and the filing of the suit.^[89]

In January 2022, the US District Court for the District of Columbia ruled that FTC has grounds to proceed with its antitrust lawsuit against Meta. With its amended lawsuit, FTC is seeking to make Meta sell its subsidiaries.^[90]

Facebook claimed that since Forrest has registered an account, he has agreed to their terms of conditions, therefore protecting them from liability.^[108]