AT&T Corporation, originally the American Telephone and Telegraph Company, is the subsidiary of AT&T Inc. that provides voice, video, data, and Internet telecommunications and professional services to businesses, consumers, and government agencies.

During its 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 was roughly US$3 billion annually.

In 2005, AT&T was purchased by Baby Bell and former subsidiary SBC Communications for more than $16 billion ($20.9 billion in present-day terms[2]). SBC then changed its name to AT&T Inc.