Modelling agricultural activities gives insight into the environmental impact of current practices. Furthermore, modelling allows testing the effect of mitigation strategies or management changes and supports decision making towards environmentally friendlier products. Model quality depends on accuracy of modelling decisions and quality of the obtained data. This chapter discusses several tools to assess model quality. The chapter categorizes agricultural models based on certain characteristics, such as linearity and time-dependence. The chapter includes two detailed case studies that show the benefits of including uncertainty propagation and sensitivity analysis. Finally, the chapter looks ahead to future trends in research and suggests further reading in this area.