Nothing is more fundamental to agriculture and our food supply than seeds. Whether eaten directly or processed through animals, seeds are the ultimate source of human nutrition.  The variety, abundance, and safety of foods are all dependent on the availability and quality of seeds.The prowess of genetic engineers notwithstanding, seeds cannot be made from scratch.  They must be harvested, saved, and shepherded from generation to generation by knowledgeable, engaged individuals.  The value to the food supply of the seeds entrusted to our generation cannot be overstated.In this report, the Union of Concerned Scientists (UCS) examines a new phenomenon that may threaten the quality of the seed supply: the contamination of traditional seeds by DNA sequences derived from genetically engineered crop varieties.  These varieties are produced by molecular techniques?variously known as genetic engineering, genetic modification, or transgenic techniques?that allow scientists to move novel traits into plants from distantly related organisms such as animals and bacteria.The number of transgenes that might potentially contaminate the seed supply is large. Although most commercial transgenic varieties of corn, cotton, soybeans, and canola contain only two traits (herbicide and insect resistance), hundreds of other novel genes have been engineered into crops that have been field tested but have not been, and may never be, commercialized.Most of the transgenes used by genetic engineers are new to foods and some are not intended for use in foods at all.  For these and other reasons, concerns have arisen about the possibility that transgenes introduced into crop varieties through genetic engineering might unintentionally contaminate the seed supply for traditional, or non-genetically engineered, varieties of crops.The research covered in this report addresses that possibility with a small pilot study of seeds of traditional varieties of three major food crops: corn, soybeans, and canola. The study found that the seeds of traditional varieties bought from the same retailers used by U.S. farmers are pervasively contaminated with low levels of DNA sequences originating in genetically engineered varieties of those crops.