A telephone company (or telco) provides telecommunications services such as telephony and data communications. Most of the largest telcos are or were at one time nationalized or state-regulated monopolies. These monopolies are often referred to, primarily in Europe, as PTTs.

Telcos are also known as common carriers and local exchange carriers. With the advent of cellular telephony, telcos now include wireless carriers.

Most telcos now also function as ISPs, and the distinction between telco and ISP may disappear completely over time.