CAN is one of the communication standards defined in the EOBD (European On-Board Diagnostics) standard, ISO 15031 and in the equivalent American OBD II standard. In Europe, EOBD has been mandated as the diagnostics standard on all new petrol vehicles sold since 2001, and all new diesel vehicles sold since 2004. By model year 2008, CAN will be the only permitted interface for OBD II diagnostics in the USA. Even without legislation in Europe, it is more than likely that the vast majority of manufacturers will follow suit and utilise CAN as the interface for providing EOBD functionality.
This article has only touched the surface of the technical features of CAN. A large amount of information can be found on the Internet.