FidoNet is a worldwide computer network that is used for communication between bulletin board systems (BBSs). It uses a store and forward system to exchange private (email) and public (forum) messages between the BBSs in the network, as well as other files and protocols in some cases. To save on long distance calling charges when those were expensive, FidoNet used a number of techniques to ensure data was compressed using the then-latest methods of data compression.

As a side-effect of its creation history, FidoNet was based on a number of small interacting programs. Only one of these interacted with the BBS system directly, and was the only portion that had to be ported to support other BBS software. As a result, FidoNet was one of the few networks that was widely supported by almost all BBS software, as well as a number of systems for talking to non-BBS online services.

The rapid improvement in modem speeds during the early 1990s, combined with the rapid decrease in price of computer systems and storage, made BBSes increasingly popular, and FidoNet along with it. By the mid-1990s it was possible to communicate with millions of users on tens of thousands of FidoNet systems around the world. Only UUCP came close in terms of breadth or numbers. The network continues to operate but has shrunk considerably, primarily due to the closing of many BBSes during the increase of popularity of the Internet.