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A leased line is a symmetric telecommunications line connecting two locations. It is sometimes known as a 'Private Circuit' or 'Data Line' in the UK. Unlike traditional PSTN lines it does not have a telephone number, each side of the line being permanently connected to the other. Leased lines can be used for telephone, data or Internet services. Some are ringdown services, and some connect two PBXes.

In the U.K., leased lines are available at speeds from 64Kb/s increasing in 64Kb/s increments to 2Mb/s over a channelised E1 tail circuit. The NTE will terminate the circuit and provide the requested presentation most frequently X.21 however higher speed interfaces are available such as G.703 or 10baseT. Some ISPs however use the term more loosely, defining a leased line as “any dedicated bandwidth service delivered over a leased fibre connection”^[1]

In the U.S., low-speed leased lines (56 kbit/s and below) are usually provided using analog modems. Higher-speed leased lines are usually presented using FT1 (Fractional T1): a T1 bearer circuit with 1 to 24 56k or 64k timeslots. Customers must manage their own network termination equipment—Channel Service Unit and Data Service Unit (CSU/DSU).

In Hong Kong, leased lines are usually available at speeds of 64k, 128k, 256k, 512k, T1 (channelized or not) or E1 (less common). Whatever the speed, telcos usually provide the CSU/DSU and present to the customer on V.35 interface.

For many purposes, leased lines are gradually being replaced by DSL and metro Ethernet.