The United States Department of Agriculture (USDA), Agricultural Research Service's (ARS) National Plant Germplasm System (NPGS) currently maintains over 18.974 accessions of mostly economically important vascular plants. It also coordinates the activities of more than 25 USDA and other seed and clonal germplasm sites, and interacts with the international germplasm community and scientific public through the Germplasm Resources Information Network (GRIN). The GRIN database contains information on all genetic resources preserved by NPGS, including accessions of both domestic and foreign origin. Though the emphasis is on major, minor, or potential crops and their wild and weedy relatives, many other categories of plants are represented including ornamentals and some rare and endangered plants. A range of data--including passport, taxonomic, descriptor, observation, evaluation, and inventory data--for each germplasm accession is available in GRIN. The taxonomic data providing the overall organization for germplasm accessions in GRIN is the focus of this paper. For information on other aspects of GRIN or NPGS see Janick (1989) or consult the GRIN database.