Technical Abstract: Grazing lands occupy one-third of the total land base in the United States (US), covering an estimated 815 acres, with over 50% of the total land base in the 17 western states of the conterminous US classified as rangeland. Rangelands represent one of the largest and most diverse land resources in the US, and encompass broad environmental gradients in temperature and precipitation. Rangelands harbor considerable potential to mitigate climate impacts resulting from rising atmospheric levels of various greenhouse gases (GHGs), such as carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) due to an extensive land area, low-input management practices, and adaptive management that facilitates active responses to highly variable within-year and between-year precipitation. Rangelands are typically characterized by short periods of high C uptake during the growing season (2-3 months) and long periods of C balance or small losses during the remainder of the year. The dominant mechanisms for GHG mitigation in rangelands will be through carbon storage in soils and by minimization of livestock-related non-CO2 emissions. For rangeland vegetation, management and local climate condition affect plant community dynamics and subsequent plant carbon inputs into soil. Long-term management for sustainable use of rangelands will depend ultimately on elucidating mechanisms driving rangeland processes to improve our ability to predict ecosystem-level responses to projected changes in temperature and precipitation.