In light of a changing climate, the international community is committed to taking action to reduce overall levels of greenhouse gas emissions. Agriculture will play an important role here given that agriculture and land use are responsible globally for around 24% of such greenhouse gas emissions. This chapter looks at the use of farm-level models to assess and mitigate the environmental impact of agriculture, with a focus on greenhouse gas emissions and livestock production. Sections are first included on the rationale for environmental modelling in agriculture and methodologies for accounting for agricultural emissions. The authors then describe a range of tools and critically assess their use for farm-level benchmarking and mitigation assessment. The chapter also discusses the technical aspects of modelling farm-level emissions and environmental impacts within the defined framework, in order to provide a synthesis of the current state of the art and a basis for the consideration of specific development objectives.