Life cycle assessment (LCA), a method that originates from the manufacturing industry, is increasingly applied to agricultural systems as a more holistic perspective and approach with respect to managing agricultural product life cycles. However, the practice of applying LCA to agricultural systems is far from being standardized. Key methodological issues remain unresolved, resulting in a plethora of ways in which LCA is applied in practice that sometimes provides conflicting results. This chapter discusses issues associated with LCA including delimitation of systems boundaries, defining the functional unit, handling co-production, and the choosing of impact assessment methods. This chapter addresses the methodology of agricultural LCA, supported by detailed case studies. Finally, the chapter looks ahead to future research trends in this area.