Increases in the concentrations of greenhouse gases, carbon dioxide (CO 2), methane (CH 4), nitrous oxide (N 2 O), and halocarbons in the atmosphere due to human activities are associated with global climate change. The concentration of N 2 O has increased by 16% since 1750. Although the atmospheric concentration of N 2 O is much smaller (314 ppb in 1998) than of CO 2 (365 ppm), its global warming potential (cumulative radiative forcing) is 296 times that of the latter in a 100-year time horizon. Currently, it contributes about 6% of the overall global warming effect but its contribution from the agricultural sector is about 16%. Of that, almost 80% of N 2 O is emitted from Australian agricultural lands, originating from N fertilisers (32%), soil disturbance (38%), and animal waste (30%). Nitrous oxide is primarily produced in soil by the activities of microorganisms during nitrification, and denitrification processes. The ratio of N 2 O to N 2 production depends on oxygen supply or water-filled pore space, decomposable organic carbon, N substrate supply, temperature, and pH and salinity. N 2 O production from soil is sporadic both in time and space, and therefore, it is a challenge to scale up the measurements of N 2 O emission from a given location and time to regional and national levels. Estimates of N 2 O emissions from various agricultural systems vary widely. For example, in flooded rice in the Riverina Plains, N 2 O emissions ranged from 0.02% to 1.4% of fertiliser N applied, whereas in irrigated sugarcane crops, 15.4% of fertiliser was lost over a 4-day period. Nitrous oxide emissions from fertilised dairy pasture soils in Victoria range from 6 to 11 kg N 2 O-N/ha, whereas in arable cereal cropping, N 2 O emissions range from <0.01% to 9.9% of N fertiliser applications. Nitrous oxide emissions from soil nitrite and nitrates resulting from residual fertiliser and legumes are rarely studied but probably exceed those from fertilisers, due to frequent wetting and drying cycles over a longer period and larger area. In ley cropping systems, significant N 2 O losses could occur, from the accumulation of mainly nitrate-N, following mineralisation of organic N from legume-based pastures. Extensive grazed pastures and rangelands contribute annually about 0.2 kg N/ha as N 2 O (93 kg/ha per year CO 2 -equivalent). Tropical savannas probably contribute an order of magnitude more, including that from frequent fires. Unfertilised forestry systems may emit less but the fertilised plantations emit more N 2 O than the extensive grazed pastures. However, currently there are limited data to quantify N 2 O losses in systems under ley cropping, tropical savannas, and forestry in Australia. Overall, there is a need to examine the emission factors used in estimating national N 2 O emissions; for example, 1.25% of fertiliser or animal-excreted N appearing as N 2 O (IPCC 1996). The primary consideration for mitigating N 2 O emissions from agricultural lands is to match the supply of mineral N (from fertiliser applications, legume-fixed N, organic matter, or manures) to its spatial and temporal needs by crops/pastures/trees. Thus, when appropriate, mineral N supply should be regulated through slow-release (urease and/or nitrification inhibitors, physical coatings, or high C/N ratio materials) or split fertiliser application. Also, N use could be maximised by balancing other nutrient supplies to plants. Moreover, non-legume cover crops could be used to take up residual mineral N following N-fertilised main crops or mineral N accumulated following legume leys. For manure management, the most effective practice is the early application and immediate incorporation of manure into soil to reduce direct N 2 O emissions as well as secondary emissions from deposition of ammonia volatilised from manure and urine. Current models such as DNDC and DAYCENT can be used to simulate N 2 O production from soil after parameterisation with the local data, and appropriate modification and verification against the measured N 2 O emissions under different management practices.