The terrestrial carbon cycle is intrinsically tied to climate, hydrology, nutrient cycles, and the production of biomass through photosynthesis. Over two-thirds of terrestrial carbon is stored below ground in soils, and a significant amount of atmospheric CO2 is processed by soils every year. Thus, soil respiration is a key process that underlies our understanding of the carbon cycle. Soil CO2 fluxes are the sum of root (autotrophic) and microbial (heterotrophic) respiration. Several factors contribute to soil respiration, including photosynthetic supply to roots, substrate quality and availability, temperature, and moisture. The extent to which these factors contribute to soil respiration and associated uncertainties in soil CO2 measurements limit our understanding of the role of soils in regional and global carbon budgets.