The Public Switched Telephone Network (PSTN) is a term used to refer to the worldwide telephone network. It is a term used to refer to the aggregate of the world's telephone networks operated by all telephony companies at a national, regional, or local level.

Typically, the term PSTN is used to refer to slightly different things depending on the context:

  • The worldwide telephony network regardless of the technology used
  • The traditional analog and circuit-switch telephony network (as opposed to VoIP technology)
  • A conventional analog telephony subscription (e.g. PSTN line)

Originally, the PSTN was a network of fixed-line analog telephony systems. However, the PSTN is now almost entirely digital in its core, and includes mobile and other networks, as well as fixed landline telephones.