Technical Abstract: The U.S. national collection of hazelnut (Corylus L.) genetic resources is preserved at the U.S. Department of Agriculture, Agricultural Research Service National Clonal Germplasm Repository at Corvallis, Oregon. The hazelnut, also commonly known as filbert, is native throughout temperate regions of the northern hemisphere and includes four tree and five shrub species. The Corvallis Repository preserves genotypes of each of these species plus about 320 named cultivars, selections, and rootstocks from more than 27 countries. These clones undergo pathogen testing and elimination procedures upon receipt. They are preserved as trees in an orchard, with on-site backup of about 10% as tissue cultures stored at 35o F. Excised seed axes of several species are cryopreserved in liquid nitrogen. A remote back-up orchard is being established in Parlier, California, to safeguard the collection. The Corvallis Repository collection is available to international collaborators for evaluation, research or breeding purposes. During the past nine years the Repository distributed more than 600 Corylus accessions to requestors in 11 countries. This germplasm was distributed as pollen, seed, scionwood, layers, plants, and tissue cultures. Germplasm can be requested from the Corvallis Repository Curator.