Technical Abstract: Orchardgrass (Dactylis glomerata L.) is indigenous to Eurasia and northern Africa, has been naturalized on nearly every continent, and is one of the top perennial forage grasses grown worldwide. Despite its distribution and uses, there is a need for improvement of value added traits that are limited by a lack of resources available for functional and comparative genetic analysis. To improve the understanding of genetic architecture of orchardgrass, and provide a template for future functional genetic research in this species, the goals of the present study were to construct an orchardgrass genetic linkage map and identify chromosomal loci associated with late heading date. A F1 population derived from a very late heading D. glomerata ssp. himalayensis parent and an early to mid-heading D. glomerata ssp. aschersoniana parent. Two parental maps were constructed with 28 cosegregation groups and seven consensus linkage groups each, and homologous linkage groups were tied together by 38 bridging markers. All but two mapped SSR markers had homologies to physically mapped rice (Oryza sativa L.) genes, and six of the seven orchardgrass linkage groups were assigned based on this putative synteny with rice. Quantitative trait loci were detected for heading date on linkage groups 2, 5, and 6 in both parental maps, explaining between 12 and 24% of the variation.