Elevated atmospheric CO2 may cause long-term changes in the productivity and species composition of the sagebrush steppe. Few studies, however, have evaluated the effects of increased CO2 on growth and physiology of species important to this ecosystem. Since the response of plants to elevated CO2 may be limited by environmental factors, soil temperature was also examined to determine if low soil temperatures limit CO2 response. To determine how CO2 and soil temperature affect the growth of species native to the sagebrush steppe, bottlebrush squirreltail [Elymus elymoides (Raf.) Swezey], Thurber needlegrass (Stipa thurberiana Piper), and Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis Beetle) were grown in ambient (374 mL L–1) or high (567 mL L–1) CO2 and low (13°C) or high (18°C) soil temperature for approximately 4 months. Although soil temperature affected the growth of squirreltail and needlegrass, temperature did not modify their response to elevated CO2. Total biomass of sagebrush was consistent across soil temperature and CO2 treatments, reflecting its slow-growing strategy. All 3 species had higher leaf water-use efficiency at elevated CO2 due to higher net photosynthesis and lower transpiration rates. We conclude that elevated CO2 and soil warming may increase the growth of grasses more than shrubs. Field studies in the sagebrush steppe are necessary to determine if differences in biomass, resulting from changes in CO2 and soil temperature, are exhibited in the field.