Musk joined the social media service Twitter in 2009, and, as @elonmusk, he became one of the most popular accounts on the site, with more than 85 million followers as of 2022. He expressed reservations about Tesla’s being publicly traded, and in August 2018 he made a series of tweets about taking the company private at a value of $420 per share, noting that he had “secured funding.” (The value of $420 was seen as a joking reference to April 20, a day celebrated by devotees of cannabis.) The following month the U.S. Securities and Exchange Commission (SEC) sued Musk for securities fraud, alleging that the tweets were “false and misleading.” Shortly thereafter Tesla’s board rejected the SEC’s proposed settlement, reportedly because Musk had threatened to resign. However, the news sent Tesla stock plummeting, and a harsher deal was ultimately accepted. Its terms included Musk’s stepping down as chairman for three years, though he was allowed to continue as CEO; his tweets were to be preapproved by Tesla lawyers, and fines of $20 million for both Tesla and Musk were levied.

Musk was critical of Twitter’s commitment to principles of free speech, in light of the company’s content-moderation policies. Early in April 2022, Twitter’s filings with the SEC disclosed that Musk had bought more than 9 percent of the company. Shortly thereafter Twitter announced that Musk would join the company’s board, but Musk decided against that and made a bid for the entire company, at a value of $54.20 a share, for $44 billion. Twitter’s board accepted the deal, which would make him sole owner of the company. Musk stated that his plans for the company included “enhancing the product with new features, making the algorithms open source to increase trust, defeating the spam bots, and authenticating all humans.” In July 2022 Musk announced that he was withdrawing his bid, stating that Twitter had not provided sufficient information about bot accounts and claiming that the company was in “material breach of multiple provisions” of the purchase agreement. Bret Taylor, the chair of Twitter’s board of directors, responded by saying that the company was “committed to closing the transaction on the price and terms agreed upon with Mr. Musk.” Twitter sued Musk to force him to buy the company. In September 2022 Twitter’s shareholders voted to accept Musk’s offer. Facing a legal battle, Musk ultimately proceeded with the deal, and it was completed in October.

Among Musk’s first acts as Twitter’s owner were to lay off about half the company and to allow users to purchase for $8 a month the blue check-mark verification, which had previously been bestowed by Twitter upon notable figures. In addition, he disbanded Twitter’s content-moderation body and reinstated many banned accounts, most notably that of former U.S. president Donald Trump, which had been suspended after the U.S. Capitol attack on January 6, 2021. Advertising revenue fell sharply as many companies withdrew their ads from the platform. Musk changed the name of the company from Twitter to X in July 2023. (Tweets became posts with the change.)