An industrial directory cannot but be a substantial volume. Industry is defined as production of goods and the variety of goods are bewilderingly large. A directory can claim to be an industrial directory only if it covers all major sectors.

Industry is a very broad field and an industrial directory would have to cover many major sectors and numerous sub-sectors to be worthy of its name. Governments have tried to implement meaningful classifications and sub-classifications of industrial sectors, to facilitate data gathering and other purposes. In the case of industrial directories, there is a proliferation of regional directories as each region seeks to publicize its industrial capabilities and seek more business.