Management practices and technologies to reduce greenhouse gas (GHG) emissions from semiarid agroecosystems need to be identified. However, current understanding of management impacts on GHG emissions is severely limited for the three major agricultural land uses characterizing semiarid agroecosystems, namely rangelands and dryland and irrigated croplands. Grazing rangelands at moderate intensities and changes in plant communities (e.g., increased shrub abundance or shifts in herbaceous composition) can result in increased soil organic carbon (SOC), but additional research is needed across different rangeland ecosystems to fully document these effects. Dryland cropping systems that combine increased cropping intensity with minimum- or no-tillage (NT) can increase SOC. Use of NT within irrigated cropping systems can also increase SOC, but at higher rates than under dryland cropping systems. Overall, there is a paucity of data on CH₄ and N₂O flux for semiarid agroecosystems, therefore limiting generalizations regarding GHG balance for different management practices. In addition to the apparent need to fill large knowledge gaps regarding management impacts on SOC change and CH₄ and N₂O flux, critical research needs in the immediate future for semiarid agroecosystems include: a) determination of plant species diversity effects in space and time on GHG emissions, b) quantification of soil inorganic C dynamics, and c) GHG emission responses under anticipated climate scenarios.