AT&T Inc. is an American multinational conglomerate holding company, headquartered at Whitacre Tower in downtown Dallas, Texas. AT&T is the world's largest telecommunications company. AT&T is the second largest provider of mobile telephone services and the largest provider of fixed telephone services in the United States, and also provides broadband subscription television services through DirecTV; combined with AT&T's legacy U-verse service, this also makes AT&T the largest pay television operator. AT&T is the second-largest company in Texas, behind ExxonMobil. As of February 2017, AT&T is the 12th largest company in the world (non-oil and overall) as measured by a composite of revenues, profits, assets and market valuation. AT&T is the largest telecommunications company in the world by revenue. As of 2017, it is also the 21st-largest mobile telecom operator in the world, with 138.8 million mobile customers. AT&T was ranked at #4 on the 2017 rankings of the world's most valuable brands published by Brand Finance.

AT&T Inc. began its history as Southwestern Bell Telephone Company, which was a subsidiary of the Bell Telephone Company founded by Alexander Graham Bell in 1880. Bell Telephone Company evolved into American Telephone and Telegraph Company in 1885 which had since rebranded to AT&T Corporation. Following the 1982 United States v. AT&T antitrust lawsuit, this resulted in the divestiture of AT&T Corp.'s ("Ma Bell") subsidiaries or Regional Bell Operating Companies ("Baby Bells"), resulting in several independent companies including Southwestern Bell Corporation . Southwestern Bell Corporation changed its name to SBC Communications Inc. in 1995. In 2005, SBC purchased former parent AT&T Corporation and took on its branding, with the merged entity naming itself AT&T Inc. and using the iconic AT&T Corp. logo and stock-trading symbol. In 2006, AT&T Inc. acquired BellSouth, the last of the independent Baby Bell, making their formerly joint venture Cingular Wireless (which had acquired AT&T Wireless in 2004) wholly owned and rebranding it to AT&T Mobility.

The current AT&T Inc. reconstitutes much of the former Bell System and includes ten of the original 22 Bell Operating Companies, along with the original long distance division.

AT&T can trace its origin back to the original Bell Telephone Company founded by Alexander Graham Bell after his invention of the telephone. One of that company's subsidiaries was American Telephone and Telegraph Company (AT&T), established in 1885, which acquired the Bell Company on December 31, 1899, for legal reasons, leaving AT&T as the main company. AT&T established a network of subsidiaries in the United States and Canada that held a government-authorized phone service monopoly, formalized with the Kingsbury Commitment, throughout most of the twentieth century. This monopoly was known as the Bell System, and during this period, AT&T was also known by the nickname Ma Bell. For periods of time, the former AT&T was the world's largest phone company.

In 1982, U.S. regulators broke up the AT&T monopoly, requiring AT&T to divest its regional subsidiaries and turning them each into individual companies. These new companies were known as Regional Bell Operating Companies, or more informally, Baby Bells. AT&T continued to operate long distance services, but as a result of this breakup, faced competition from new competitors such as MCI and Sprint.

Southwestern Bell was one of the companies created by the breakup of AT&T Corp. The architect of divestiture for Southwestern Bell was Robert G. Pope. The company soon started a series of acquisitions. This includes the 1987 acquisition of Metromedia mobile business and the acquisition of several cable companies in the early 1990s. In the later half of the 1990s, the company acquired several other telecommunications companies, including some Baby Bells, while selling its cable business. During this time, the company changed its name to SBC Communications. By 1998, the company was in the top 15 of the Fortune 500, and by 1999 the company was part of the Dow Jones Industrial Average (lasting through 2015).

In 2005, SBC purchased AT&T for $16 billion. After this purchase, SBC adopted the better-known AT&T name and brand, with the original AT&T Corp. still existing as the long-distance landline subsidiary of the merged company. The current AT&T claims the original AT&T Corp.'s history (dating to 1885) as its own, though its corporate structure only dates from 1983. It also retains SBC's pre-2005 stock price history, and all regulatory filings prior to 2005 are for Southwestern Bell/SBC, not AT&T Corp.

In September 2013, AT&T Inc. announced it would expand into Latin America through a collaboration with Carlos Slim's América Móvil. In December 2013, AT&T announced plans to sell its Connecticut wireline operations to Stamford-based Frontier Communications.

AT&T purchased the Mexican carrier Iusacell in late 2014, and two months later purchased the Mexican wireless business of NII Holdings, merging the two companies to create AT&T Mexico.

In July 2015, AT&T purchased DirecTV for $48.5 billion, or $67.1 billion including assumed debt, subject to certain conditions. AT&T subsequently announced plans to converge its existing U-verse home internet and IPTV brands with DirecTV, to create AT&T Entertainment.

In an effort to increase its media holdings, on October 22, 2016, AT&T announced a deal to buy Time Warner for $108.7 billion.

AT&T also owns approximately a 2% stake in Canadian-domiciled entertainment company Lionsgate.

On July 13, 2017, it was reported that AT&T is going to introduce a cloud-based DVR streaming service as part of its effort to create a unified platform across DirecTV and its DirecTV Now streaming service, with U-verse to be added soon.

On September 12, 2017, it was reported that AT&T is planning to launch a brand new cable TV-like service for delivery over-the-top over its own or a competitor's broadband network sometime next year.

Of the twenty-four companies that were part of the Bell System, ten are a part of the current AT&T:

The following companies have become defunct or were sold under SBC/AT&T ownership:

AT&T stated that it would declare the intentions for its rural landlines on November 7, 2012. AT&T had previously announced that it was considering a sale of its rural landlines, which are not wired for AT&T's U-verse service; however, it has also stated that it may keep the business after all.

AT&T was not the first Baby Bell to sell off rural landlines. Ameritech sold some of its Wisconsin lines to CenturyTel in 1998; BellSouth sold some of its lines to MebTel in the 2000s; U S WEST sold many historically Bell landlines to Lynch Communications and Pacific Telecom in the 1990s; Verizon sold many of its New England lines to FairPoint in 2008 and its West Virginia operations to Frontier Communications in 2010.

On October 25, 2014, Frontier Communications took over control of the AT&T landline network in Connecticut after being approved by state utility regulators. The deal was worth about $2 billion, and included Frontier inheriting about 2,500 of AT&T's employees and many of AT&T's buildings.

AT&T Inc. has retained the holding companies it has acquired over the years resulting in the following corporate structure:

The company is headquartered at Whitacre Tower in downtown Dallas, Texas. On June 27, 2008, AT&T announced that it would move its corporate headquarters from downtown San Antonio to One AT&T Plaza in downtown Dallas. The company said that it moved to gain better access to its customers and operations throughout the world, and to the key technology partners, suppliers, innovation and human resources needed as it continues to grow, domestically and internationally. AT&T Inc. previously relocated its corporate headquarters to San Antonio from St. Louis, Missouri, in 1992, when it was then named Southwestern Bell Corporation. The company's Telecom Operations group, which serves residential and regional business customers in 22 U.S. states, remains in San Antonio. Atlanta, Georgia, continues to be the headquarters for AT&T Mobility, with significant offices in Redmond, Washington, the former home of AT&T Wireless. Bedminster, New Jersey, is the headquarters for the company's Global Business Services group and AT&T Labs. St. Louis continues as home to the company's Directory operations, AT&T Advertising Solutions.

AT&T offers also services in many locations throughout the Asia Pacific; its regional headquarters is located in Hong Kong. The company is also active in Mexico, and it was announced on November 7, 2014, that Mexican carrier Iusacell is being acquired by AT&T. The acquisition was approved in January 2015. On April 30, 2015, AT&T acquired wireless operations Nextel Mexico from NII Holdings (now AT&T Mexico).

AT&T's current board of directors as of November 2016:

The current management as of August 2017 includes:

According to the Center for Responsive Politics, AT&T is the second-largest donor to United States political campaigns, and the top American corporate donor, having contributed more than US$47.7 million since 1990, 56% of which went to Republicans and 44% of which went to Democrats. As an example, in 2005, AT&T was among 53 entities that contributed the maximum of $250,000 to the second inauguration of President George W. Bush. Bill Leahy, representing AT&T, sits on the Private Enterprise Board of the American Legislative Exchange Council (ALEC). ALEC is a nonprofit organization of conservative state legislators and private sector representatives that drafts and shares model state-level legislation for distribution among state governments in the United States.

During the period of 1998 to 2010, the company expended US$130 million on lobbying in the United States. A key political issue for AT&T has been the question of which businesses win the right to profit by providing broadband internet access in the United States. The company has also lobbied in support of several federal bills. AT&T supported the Federal Communications Commission Process Reform Act of 2013 (H.R. 3675; 113th Congress), a bill that would make a number of changes to procedures that the U.S. Federal Communications Commission (FCC) follows in its rulemaking processes. The FCC would have to act in a more transparent way as a result of this bill, forced to accept public input about regulations. AT&T's Executive Vice President of Federal Relations, Tim McKone, said that the bill's "much needed institutional reforms will help arm the agency with the tools to keep pace with the Internet speed of today's marketplace. It will also ensure that outmoded regulatory practices for today's competitive marketplace are properly placed in the dustbin of history."

The financial performance of the company is reported to shareholders on an annual basis and a matter of public record. The unit (except where noted) is billions of US dollars. Where performance has been restated, the most recent statement of performance from an annual report is used.

The company maintains a database of call detail records of all telephone calls that have passed through its network since 1987. AT&T employees work at High Intensity Drug Trafficking Area offices (operated by the Office of National Drug Control Policy) in Los Angeles, Atlanta, and Houston so data can be quickly turned over to law enforcement agencies. Records are requested via administrative subpoena, without the involvement of a court or grand jury.

In September 2007, AT&T changed its legal policy to state that "AT&T may immediately terminate or suspend all or a portion of your Service, any Member ID, electronic mail address, IP address, Universal Resource Locator or domain name used by you, without notice for conduct that AT&T believes ... (c) tends to damage the name or reputation of AT&T, or its parents, affiliates and subsidiaries." By October 10, 2007, AT&T had altered the terms and conditions for its Internet service to explicitly support freedom of expression by its subscribers, after an outcry claiming the company had given itself the right to censor its subscribers' transmissions. Section 5.1 of AT&T's new terms of service now reads "AT&T respects freedom of expression and believes it is a foundation of our free society to express differing points of view. AT&T will not terminate, disconnect or suspend service because of the views you or we express on public policy matters, political issues or political campaigns."

In 2006, the Electronic Frontier Foundation lodged a class action lawsuit, Hepting v. AT&T, which alleged that AT&T had allowed agents of the National Security Agency (NSA) to monitor phone and Internet communications of AT&T customers without warrants. If true, this would violate the Foreign Intelligence Surveillance Act of 1978 and the First and Fourth Amendments of the U.S. Constitution. AT&T has yet to confirm or deny that monitoring by the NSA is occurring. In April 2006, a retired former AT&T technician, Mark Klein, lodged an affidavit supporting this allegation. The Department of Justice has stated it will intervene in this lawsuit by means of State Secrets Privilege.

In July 2006, the United States District Court for the Northern District of California – in which the suit was filed – rejected a federal government motion to dismiss the case. The motion to dismiss, which invoked the State Secrets Privilege, had argued that any court review of the alleged partnership between the federal government and AT&T would harm national security. The case was immediately appealed to the Ninth Circuit. It was dismissed on June 3, 2009, citing retroactive legislation in the Foreign Intelligence Surveillance Act.

In May 2006, USA Today reported that all international and domestic calling records had been handed over to the National Security Agency by AT&T, Verizon, SBC, and BellSouth for the purpose of creating a massive calling database. The portions of the new AT&T that had been part of SBC Communications before November 18, 2005, were not mentioned.

On June 21, 2006, the San Francisco Chronicle reported that AT&T had rewritten rules on its privacy policy. The policy, which took effect June 23, 2006, says that "AT&T – not customers – owns customers' confidential info and can use it 'to protect its legitimate business interests, safeguard others, or respond to legal process.'"

On August 22, 2007, National Intelligence Director Mike McConnell confirmed that AT&T was one of the telecommunications companies that assisted with the government's warrantless wire-tapping program on calls between foreign and domestic sources.

On November 8, 2007, Mark Klein, a former AT&T technician, told Keith Olbermann of MSNBC that all Internet traffic passing over AT&T lines was copied into a locked room at the company's San Francisco office – to which only employees with National Security Agency clearance had access.

AT&T keeps for five to seven years a record of who text messages whom and the date and time, but not the content of the messages.

In January 2008, the company reported plans to begin filtering all Internet traffic which passes through its network for intellectual property violations. Commentators in the media have speculated that if this plan is implemented, it would lead to a mass exodus of subscribers leaving AT&T, although this is misleading as Internet traffic may go through the company's network anyway. Internet freedom proponents used these developments as justification for government-mandated network neutrality.

AT&T is accused by community media groups of discriminating against local Public, educational, and government access (PEG) cable TV channels, by "impictions that will severely restrict the audience".

According to Barbara Popovic, Executive Director of the Chicago public-access service CAN-TV, the new AT&T U-verse system forces all Public-access television into a special menu system, denying normal functionality such as channel numbers, access to the standard program guide, and DVR recording. The Ratepayer Advocates division of the California Public Utilities Commission reported: "Instead of putting the stations on individual channels, AT&T has bundled community stations into a generic channel that can only be navigated through a complex and lengthy process."

Sue Buske (president of telecommunications consulting firm the Buske Group and a former head of the National Federation of Local Cable Programmers/Alliance for Community Media) argue that this is "an overall attack [...] on public access across the [United States], the place in the dial around cities and communities where people can make their own media in their own communities".

In June 2010, a hacker group known as Goatse Security discovered a vulnerability within AT&T that could allow anyone to uncover email addresses belonging to customers of AT&T 3G service for the Apple iPad. These email addresses could be accessed without a protective password. Using a script, Goatse Security collected thousands of email addresses from AT&T. Goatse Security informed AT&T about the security flaw through a third party. Goatse Security then disclosed around 114,000 of these emails to Gawker Media, which published an article about the security flaw and disclosure in Valleywag. Praetorian Security Group criticized the web application that Goatse Security exploited as "poorly designed".

In April 2015, AT&T was fined $25m over data security breaches, marking the largest ever fine issued by the Federal Communications Commission (FCC) for breaking data privacy laws. The investigation revealed the theft of details of approximately 280,000 people from call centres in Mexico, Colombia and the Philippines.

In March 2012, the United States federal government announced a lawsuit against AT&T. The specific accusations state that AT&T "violated the False Claims Act by facilitating and seeking federal payment for IP Relay calls by international callers who were ineligible for the service and sought to use it for fraudulent purposes. The complaint alleges that, out of fears that fraudulent call volume would drop after the registration deadline, AT&T knowingly adopted a non-compliant registration system that did not verify whether the user was located within the United States. The complaint further contends that AT&T continued to employ this system even with the knowledge that it facilitated use of IP Relay by fraudulent foreign callers, which accounted for up to 95 percent of AT&T's call volume. The government's complaint alleges that AT&T improperly billed the TRS Fund for reimbursement of these calls and received millions of dollars in federal payments as a result."

On April 28, 2015, AT&T announced that it had fired Aaron Slator, President of Content and Advertising Sales, for sending racist text messages. Slator was also hit with a $100 million discrimination lawsuit, filed by African-American employee Knoyme King. The day before that, protesters arrived at AT&T's headquarters in Dallas and its satellite offices in Los Angeles as well as at the home of CEO Randall Stephenson to protest alleged systemic racial policies. According to accounts, the protesters are demanding AT&T begin working with 100% black-owned media companies.

In June 2016, Citigroup sued AT&T for trademark infringement, false designation of origin, and unfair competition. The company had recently established a loyalty program under the brand AT&T Thanks, which Citigroup claims would cause consumer confusion as an infringement of its "ThankYou" and "Citi ThankYou" marks due to similar wording and visual design. Citi, which also provides a co-branded credit card for AT&T that links with its ThankYou rewards program, sought unspecified damages and the expungement of AT&T's trademark registration.

The suit was dismissed in August 2016, with a judge ruling that there was a low likelihood of confusion between the two marks because the companies fall within different industries, and that consumers who use loyalty programs would be able to "clearly take into account the attributes associated with the products they purchase" and, thus, be able to distinguish them.