AT&T Corporation, an abbreviation for its former name, the American Telephone and Telegraph Company, was an American telecommunications company that provided voice, video, data, and Internet telecommunications and professional services to businesses, consumers, and government agencies.

During the Bell System's long history, AT&T was at times the world's largest telephone company, the world's largest cable television operator, and a regulated monopoly. At its peak in the 1950s and 1960s, it employed one million people and its revenue ranged between US$3 billion in 1950 ($42.6 billion in present-day terms) and $12 billion in 1966 ($120 billion in present-day terms).

In 2005, AT&T was acquired by "Baby Bell" and former subsidiary SBC Communications for more than $16 billion ($25.8 billion in present-day terms). SBC then changed its name to AT&T Inc., with AT&T Corporation continuing to exist as a long-distance calling subsidiary until its dissolution on May 1, 2024.