Private automatic branch exchange (PABX) is a technology used by call centers and other large organizations that allows a single access number to provide several lines to outside callers while providing a range of external lines to internal callers or staff. PABX performs all the switching necessary for making internal calls between extensions within the organizations. It also allows provides a connection between extensions and external phone lines.

In PABX, the exchange is owned and managed by the private organization in which it is installed and relies on computer equipment to handle the switching of calls. This is why the system is considered both private and automatic.

With PABX, an operator is only required to supply information and to occasionally manual connections for callers who are unfamiliar with system or the organization.