Technical Abstract: Western wheatgrass (Pascopyrum smithii [Rydb.] A. Love) has low seed production and poor germination and seedling vigor, limiting its use when quick establishment is needed to stabilize degraded rangelands. This study examined differences among germplasm sources and determined effects of seed production environment on western wheatgrass seed traits. Seed was harvested from 10 western wheatgrass cultivars and germplasms grown in three environments. Seed yield, seed weight, seedling germination, and seedling vigor were then determined. Seedling vigor was measured by greenhouse evaluation of seedling emergence percentage and rate from a planting depth of 6.35 cm. There was a significant cultivar x environment interaction for seed yield and seed weight, but relatively high Spearman's rank correlations (0.64 to 0.85) suggested that environment had only a moderate effect on ranking of cultivars. Mean seed yield and 100-seed weight varied significantly among cultivars, ranging from 2.6 to 25.4 g plant-1, and 0.43 to 0.54 g, respectively. Seed germination was high, ranging from 78.4 to 94.4%; however, cultivar performance was not consistent across environments. Environment had no effect on seedling emergence rate, whereas emergence among cultivars ranged from 2.4 to 4.2 seedlings d-1. Germination rate and seed weight were both correlated with seedling emergence rate (r=0.57 and 0.49, respectively). These results indicated that the seed production environment had little effect on western wheatgrass seed yield or seedling vigor, and that may be possible to breed for improvement in these traits by selecting among and within western wheatgrass cultivars.