This text guides its readers through the development and specification of the world standard Fieldbus. The Fieldbus was originally designed to be the industrial control standard for high integrity, low- level communication between sensors, actuators and local controllers on the factory shop floor or in the process plant. Its specification has been enhanced to enlarge the potential market place to include the control room or "cell level" plus many other applications outside its core area. This text is aimed at all those involved with this standard from end users to equipment suppliers.