An analysis of the impact of simulation modelling in three diverse crop-livestock improvement projects in Agricultural Research for Development (AR4D) reveals benefits across a range of aspects including identification of objectives, design and implementation of experimental programs, effectiveness of participatory research with smallholder farmers, implementation of system change and scaling-out of results. In planning change, farmers must consider complex interactions within both biophysical and socioeconomic aspects of their crop and animal production activities. For this, whole-farm models that include household models of food, workload and financial requirements have the most utility and impact. The analysis also proposes improvements in design and implementation of AR4D projects to improve the utility of simulation modelling for securing positive agronomic and livestock outcomes and lasting legacies.