Cincinnati Bell, Inc., doing business as Altafiber, is a regional telecommunications service provider based in Cincinnati, Ohio, United States. It provides landline telephone, fiber-optic Internet, and IPTV services through its subsidiaries Altafiber Home Phone and Hawaiian Telcom, which are the incumbent local exchange carriers for the Greater Cincinnati metropolitan area (aka "The Tri-State") and Hawaii. Other subsidiaries provide enterprise information technology services and long distance calling.

Cincinnati Bell was founded in 1873 as a telegraph company and for much of its history was a Bell System franchisee. In the 1990s, Cincinnati Bell expanded into Internet access and mobile phone services. The company divested its mobile phone service in 2014 to focus on enterprise and fiber-optic services. It was acquired in September 2021 by Australia's Macquarie Infrastructure and Real Assets, and began doing business as Altafiber in March 2022.

Cincinnati Bell was founded as the City and Suburban Telegraph Association on July 5, 1873. Founder Charles Kilgour had run the Cincinnati Street Railway with his brother John but became homebound after an accident and began running his business from home via telegraph. The City and Suburban Telegraph Association ran telegraph lines between homes and businesses beginning in 1873, three years before the invention of the telephone. In 1878, it gained exclusive rights to the Bell franchise within a 25-mile (40 km) radius of Cincinnati, becoming the first telephone exchange in Ohio and the tenth in the United States. It has substantially the same three-state incumbent local exchange carrier territory today. On August 21, 1877, it signed its first telephone customer, the Cincinnati Gas-Light and Coke Company (later known as Cincinnati Gas and Electric).

The company was renamed Cincinnati and Suburban Bell Telephone Company in 1903.

From 1930 to 1952, the company converted its exchanges from staffed switchboards to dial service. Seven-digit dialing was introduced in 1962. In 1968, electromechanical switching equipment was replaced by one of the first electronic switching systems. The company formally simplified its name to Cincinnati Bell in 1971.

In May 1999, the Public Utilities Commission of Ohio awarded Cincinnati Bell Long Distance the right to offer local wireline telephone service in 55 counties outside its incumbent territory and the company began to resell business local phone service in these counties, in competition with incumbent carrier Ameritech.

During the 1990s, Cincinnati Bell acquired a nationwide transmission network formerly known as IXC Communications and changed its corporate name to "Broadwing Communications", although the local telephone operations continued to operate under the traditional Cincinnati Bell name. The acquisition fell short of expectations due to intense competition and lackluster demand and left Broadwing with over $2 billion in debt. In 2004, the holding company divested the long-distance operation as Broadwing Corporation and changed its name back to Cincinnati Bell. Broadwing Corporation was later acquired by Level 3 Communications.

In 2002, Cincinnati Bell sold Cincinnati Bell Directory, consisting of its directory operations, to Spectrum Equity. The resulting company is named CBD Media. The sale marked the first time a former Bell System-affiliated company had sold off its directory operations. In 2003, when BellSouth exited the payphone market, some former BellSouth payphones in Kentucky were sold to Cincinnati Bell.