CenturyLink, Inc. is a United States telecommunications firm, headquartered in Monroe, Louisiana. The company, founded as Central Telephone & Electronics Corporation in 1968, later changed its name to Century Telephone Enterprises, Inc. in 1971, and then was called CenturyTel, Inc. from 1999 to 2010. A member of the S&P 500 index, the company operates as a local exchange carrier and Internet service provider in U.S. markets and is the third-largest local exchange carrier in the U.S. in terms of lines served. It also provides long distance service.