Evaluation and mitigation of greenhouse gas emissions from dairy farms requires a comprehensive approach that integrates the impacts and interactions of all important sources and sinks. This approach requires some form of modeling. Types of models commonly used include empirical emission factors, process-based emission factors and process-level simulation. If properly applied, each type can be useful in evaluating dairy farm emissions. Important emission sources include the animal, manure in the housing facility, manure storage, pasture and cropland soil, and machinery operations. Important gases emitted are methane (CH₄), nitrous oxide (N₂O) and carbon dioxide (CO₂). Methane and N₂O are normally converted to CO₂ equivalents using a global warming index and summed with anthropogenic CO₂ to get a total net emission. From a global warming perspective, enteric CH₄ from the animals is normally the major dairy farm source followed by manure storage emissions and soil emissions during feed crop production. Emissions from a free stall barn are small, but those from open lots or bedded pack facilities become more important. Manure storage is often an important source where storage type, manure dry matter content and temperature have a major effect on the amount and form of emissions. Nitrous oxide emissions from pasture and cropland can also be important due to the high global warming potential of this gas. These emissions are related to temperature and the nitrogen and moisture contents of the soil. Anthropogenic CO₂ emissions from fuel combustion and lime decomposition are relatively small compared with other sources, but they are still important. Ammonia is also an important emission. It is not a greenhouse gas, but some of the ammonia and nitrates lost to the environment are transformed to N₂O providing an indirect emission source. For a full accounting, emissions occurring during the production of resources used on the farm, such as fuel, electricity, fertilizer and feed, must also be considered. Models representing the integration of these sources have become important tools for assessing best management practices to mitigate dairy farm emissions.