A landline or main line is a telephone line which travels through a physical, land-based medium. This is distinguished from a mobile cellular line, where the medium used is the airwaves. A land line is also usually used to increase the security of communications, as it can not 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 844 million main telephone lines worldwide. China had more than any other country, at 263 million, and the United States was second with 181.6 million. This compared with 158.7 million cellular telephones, a number which is expected to exceed the main line number within a few years.