Technical Abstract: Forage nitrogen (N) and nonstructural carbohydrate (NSC) concentrations are important indicators of forage quality, and knowledge of N and NSC variation among grass germplasm is one element to consider in developing a successful forage and livestock management program. An experiment was conducted in 2004 and 2005 at the USDA-ARS, Grazinglands Research Laboratory, El Reno, OK to investigate concentrations of N, neutral detergent fiber (NDF), acid detergent fiber (ADF), glucose, fructose, sucrose, fructans, and starch in 13 perennial cool-season grass entries from five plant species at the heading stage. Entries from tall fescue (Festuca arundinacea L. cv. Carmine, Dovey, Kentucky 31, and Maximize), festulolium (F. arundinacea × L. multiflorum, cv. Felina and Hykor), tall wheatgrass (Elytrigia elongate, cv. Jose), intermediate wheatgrass (Elytrigia intermedia, cv. Luna and Manska), and smooth bromegrass [Bromus inermis, cv. Lincoln and three experimental lines (Lincoln YD, NE B1-2-C0, and NE B1-2-C2) developed at the USDA-ARS, Lincoln, NE] were established in 2000. Year and grass species influenced both forage N and NSC concentrations. Total NSC around heading stage ranged from 70 to 112 g/kg (dry weight basis) among the 13 entries. Smooth bromegrass had the highest and tall wheatgrass the lowest total NSC concentration, but changes in the fraction of each carbohydrate in total NSC were relatively small among the five species. Averaged across the entries, glucose, fructose, sucrose, fructans, and starch accounted for 14, 10, 15, 38, and 23% of total NSC, respectively. The NSC information from this study can help breeders and producers select appropriate cool-season grass varieties for livestock.