The Grain & Graze Whole-Farm Model was developed as a simple modelling tool to identify better strategies to improve the income of farmers and overcome grassland degradation. Using information on farm structure, crop and forage production systems, livestock production systems and variable costs involved in all enterprises, maximum whole-farm gross margins are obtained for an optimum or a prescribed mix of enterprises. The incorporation of production systems for different rainfall scenarios enables climatic risks and water use efficiencies of different enterprises to be investigated. Model simulations demonstrated the potential improvements that could be achieved in dollar water use efficiency ($WUE), by changes in management and/or changes in enterprise. The design of the model makes it a valuable tool for evaluating new systems, as it easy to develop new crop, pasture and livestock systems. Innovative farming systems such as pasture cropping and alley farming are included in the model.