Technical Abstract: A study was conducted to examine the foraging range of honey bees in an agroecosystem dominated by a glyphosate-resistant Roundup Ready® (RR) alfalfa seed production field and several non-RR fields. Honey bee self-marking devices were attached to colonies originating from nine different apiary locations. The foraging bees exiting each apiary location were uniquely tagged so that the apiary of origin and the distance traveled by field-collected bees could be measured. Honey bee self-marking devices were installed on about 13% of the total hives located within the research area. The frequency of field-collected bees possessing a distinct mark was similar, averaging about 14%. Over 12,000 bees were collected from the various alfalfa fields on seven sampling dates over the course of the two year study. The distances traveled by marked bees ranged from a minimum of 148 feet to a maximum of 3.7 miles. On average, marked bees dispersed a half mile from their apiary of origin and the recovery rate of marked bees decreased exponentially as the distance from the apiary increased. Ultimately these data were used to identify the extent of pollen-mediated gene flow from RR to conventional alfalfa (see Teuber et al., herein).