Crop-livestock farming systems integrate various biophysical components with farm decision-making. Whole-farm system models help to understand the complexity arising from this integration and are useful tools to explore effects of interventions and to design improved systems. After describing the generic characteristics of crop-livestock systems, this chapter gives an account of the separate component models, from which whole-farm models are usually assembled. Most attention goes to the wide diversity in pasture, livestock and manure models, while approaches to represent farm management in models are also discussed. The interactions between farm components strongly determine model functioning and performance, and often present modelling challenges to capture them. With a focus on grazing, manure dynamics and animal mobility, the authors assess the key processes governing these interactions and review how models represent them. Further, the representation of feed quality in crop model outputs and the management of time scales and carry-over effects is dealt with. Finally, the authors provide two examples of common whole-farm model applications from contrasting environments.