Asterisk was created in 1999 by Mark Spencer of Digium, which, since 2018, has been a division of Sangoma Technologies Corporation.

Users can create new functionality by writing dial plan scripts in several of Asterisk's own extensions languages by adding custom loadable modules written in PHP or C or by implementing Asterisk Gateway Interface (AGI) programs using any programming language capable of communicating via the standard streams system (stdin and stdout) or by network TCP sockets.

It can serve as a gateway between IP phones and the PSTN via T- or E-carrier interfaces or analog FXO cards.

Many VoIP service providers support it for call completion into the PSTN, often because they themselves have deployed Asterisk or offer it as a hosted application.

Some sites are using Asterisk to replace proprietary PBXes, others provide additional features, such as voice mail or voice response menus, or virtual call shops, or to reduce cost by carrying both local and long-distance calls over the Internet.

The default set of English-language Asterisk prompts are recorded by professional telephone voice Allison Smith.