A landline, main line or fixed-line is a telephone line which travels through a solid medium, either metal wire or optical fibre. This is distinguished from a mobile cellular line, where the medium used is the airwaves. Landlines usually cost less than cellular lines and provide better voice quality, and are used when there is no need for mobility or where cellular service is unavailable. A land line is also used to increase the security of communications, as it cannot be intercepted by a receiver without physical access to the line. (This does not, however, mean that a telephone company will not send the call over the air on some point in the journey.)

In 2003, the CIA reported approximately 1263 million main telephone lines worldwide. China had more than any other country, at 350 million, and the United States was second with 268 million - this compared with 219.4 million cellular telephones, a number which is expected to exceed the landline number within a few years.