The present invention relates to a field device for automation technology. Said field device is accommodated in a housing which is produced from a polygonal profile and, for its part, is closed by a base plate and a cover plate. A base module is connected to the base plate, said base module being provided in a manner designed in the same way in all devices of a field bus, in order to manage the tasks of voltage supply and network connection. A functional module, which is optionally connected to the cover plate, provides the field device with one or more specific functionalities, and therefore configures the field device in a specific direction. This results in a unit of modular construction which, together with other identical field devices of different configuration, can be joined in accordance with the construction kit principle to form an automation system.