The emerging IEC 'Fieldbus' standard is intended to define a serial communications network for interfacing to low-level devices in factories or process plants, including sensors, actuators, single-variable controllers and small (often embedded) computers. Fieldbus has lower bit rates than those of, say, MAP or miniMAP networks but its features address a range of requirements which are important at the lowest level of automated control, including realtime response, low cost, intrinsic safety and a powered bus. The paper considers some of the technical challenges which a local area network used within an industrial environment will have to meet and, in particular, considers the developing IEC Fieldbus standard and its relationship to MAP, miniMAP and other proprietary field buses.