MCI Communications Corporation (MCI) was one of the largest telecommunications companies in the world. It was incorporated in Delaware in 1968 as Microwave Communications of America, Inc., to provide businesses with nationwide microwave telecommunications services at low prices. Being confronted by industry de facto monopoly AT&T in the interconnection of its lines to local facilities owned by AT&T affiliated regional Bell companies, MCI challenged the telecommunications giant with competitive long-distance telephone services, both in courts and at the marketplace. MCI-AT&T antitrust litigation (1974-1985) led to AT&T's divestiture of its regional carriers and changed the previously regulated telecommunications industry into a business open to competition. The collection documents all facets of MCI history from 1968 to the end of the 1990s, as well as changes in the American telecommunications regulatory policy, legislation, and public perception of the industry. Documents also include records of MCI's subsidiaries and their predecessors starting as early as 1849.