Pennsylvania is the fourth largest dairy producer in the U.S. High quality alfalfa is essential to dairy production with Pennsylvania ranking 15^th nationwide in alfalfa production. Weed management in alfalfa is complex because both interference and quality must be considered. In general, effective herbicides are available for grassy weeds, while broadleaf species remain more difficult to manage. The use of glyphosate in glyphosate-resistant Roundup Ready alfalfa potentially offers unprecedented weed control and crop safety, and is expected to be available commercially in the near future. However, with the introduction of any new agricultural technology, efficacy and management validation must be provided prior to its release. Experiments were initiated starting in 2002 in Pennsylvania examining weed control, crop tolerance, and alfalfa performance. Additional studies in 2004 examined control of Roundup Ready alfalfa in rotation to no-till corn, the potential for Roundup Ready alfalfa/grass mixtures, and weed competition in first year Roundup Ready alfalfa. These experiments aim to provide an understanding of the Roundup Ready alfalfa system and how it could be implemented in Pennsylvania. Herbicide tolerance studies showed good crop tolerance during the establishment year at the highest rate applied; 3.0 lb ae/ac of glyphosate applied four times during the establishment year. Alfalfa forage yield remained unchanged at the highest glyphosate rate and weed control with glyphosate was equal or better than the competitive products. In first-year alfalfa/grass mixtures not treated with glyphosate, orchardgrass (Dactylis glomerata) dry matter was lower and weed dry matter was higher than when orchardgrass was seeded following a post-emergence glyphosate application. Preliminary results from the weed competition and critical period of weed control research show the benefit of timely weed control on alfalfa crop yield. In summary, initial observations show that Roundup Ready alfalfa could be a successful addition to weed management for alfalfa in Pennsylvania.