In setting out to establish standards for data fields in botanical databases, the International Working Group on Taxonomic Databases for Plant Sciences (TDWG) identified at an early stage of its existence a need for an agreed system of geographical units at approximately "country" level and upwards for use in recording plant distributions. This would aim to provide a standard which different organisations maintaining databases could adopt so that they could compare and exchange data with each other without loss of information due to incompatible geographical boundaries. The present publication has resulted from the deliberations over a period of three years of a committee of both taxonomic and applied botanists set up to produce such a standard. The system offered covers the whole world and identifies units at four levels, firstly continental, secondly regional (or subcontinental), thirdly at what may be called "Botanical Country" level (which may often ignore purely political considerations), and fourthly at a slightly lower level called "Basic Recording Units" where political integrity is fully recognised. In many cases, where Botanical Countries have no complicating political factors, the units at Level-3 and Level-4 are identical. Very large countries, however, have been subdivided into more conveniently sized units according to constituent states or provinces. It is a fundamental principle that units at all levels are bounded either by political boundaries which appear on modern maps or by coast lines. Modern geographical information systems have not superseded the need for such a scheme. While this standard is still in use, it is no longer actively maintained (labelled as prior on the TDWG website).