MCI, Inc. (d/b/a Verizon Business) was an American telecommunication corporation, currently a subsidiary of Verizon Communications, with its main office in Ashburn, Virginia. The corporation was formed originally as a result of the merger of WorldCom and MCI Communications corporations, and used the name MCI WorldCom, succeeded by WorldCom, before changing its name to the present version on April 12, 2003, as part of the corporation's ending of its bankruptcy status. The company traded on NASDAQ as WCOM (pre-bankruptcy) and MCIP (post-bankruptcy). The corporation was purchased by Verizon Communications with the deal finalizing on January 6, 2006, and is now identified as that company's Verizon Enterprise Solutions division with the local residential divisions being integrated slowly into local Verizon subsidiaries.

MCI Communications Corp. was an American telecommunications company that was instrumental in legal and regulatory changes that led to the breakup of the AT&T monopoly of American telephony and ushered in the competitive long-distance telephone industry. It was headquartered in Washington, D.C.