Technical Abstract: The US collection of Medicago species is maintained by the USDA National Plant Germplasm System located in Pullman, Washington. The current collection contains a total of 7,554 accessions with 4,108 perennial and 3,446 annual accessions. The beginning of the collection traces back to N. E. Hansen and his collection in Russia in 1898. The collection has been evaluated for 14 diseases, 6 insects, 25 agronomic traits, chromosome number, 7 feed quality traits, and 5 stress tolerant traits. Core subsets have been developed for the perennial and annual species. Early in the history of alfalfa cultivar development, accessions within the collection were evaluated and selections made of the best and released as cultivars, however, currently a majority of the modern alfalfa cultivars have arisen from preexisting cultivars or germplasm pools. The majority of requested germplasm is intended for applied and basic research projects. The collection utilizes the advise and talents of an Alfalfa Crop Germplasm Committee which consists of 21 members representing federal, state and private interests. The Medicago collection is an international treasure which requires continued vigilance in maintaining the current collection.