Our own morphological examinations are based on about ¾ of all Cupressaceae species and a careful compilation of the relevant bibliography. All data collected from our own examinations and the bibliographies were entered into a DELTA matrix. The literature data are based on a careful compilation of more than 600 literature sources, including more than 10,000 taxon descriptions (e.g. type descriptions, improved descriptions, floras and morphological examinations. Our own morphological examinations were made on specimens from botanical gardens, the natural environment and herbariums. The data were collected using a standardized questionaire to receive as much information as possible and to simplify the collecting. These lists ensured the compatibility of all data. In contrast to many other descriptions, in our key we tried to avoid subjective characters. The variability of the character states was extended to the maximum maximum resulting from the different sources. Many descriptions in the bibliography give a too narrow character variability which can not reflect the whole variability in the natural habitat. It is precisely described where the mentioned characters can be found. Where ever possible, each piece of information is an assessment of information from different sources.