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.

Founded in 1963, it grew to be the second largest long-distance provider in the U.S. It was purchased by WorldCom in 1998 and became MCI WorldCom, and afterwards being shortened to WorldCom in 2000. WorldCom's financial scandals and bankruptcy led that company to change its name in 2003 to MCI. The MCI name disappeared in January 2006 after the company was bought by Verizon.