Development of a simulation model of the dairy forage system began in the early 1980’s. The model, known as the Dairy Forage System Model or DAFOSYM, linked alfalfa and corn production models with a dairy animal intake model to predict feed production and disappearance on the farm. This model was expanded with additional components for simulating feed storage and animal performance. Manure handling, tillage, and planting operations were then added to extend the model to a simulation of the full dairy farm. The dairy farm model was broadened further by adding components for simulating grass, small grain, and soybean growth, harvest, and storage. Through a major revision, a beef animal component was added along with a crop farm option (no animals) to form the Integrated Farm System Model or IFSM. This model has continued to grow as components were added to simulate environmental impacts including ammonia volatilization, nitrate leaching, phosphorus runoff, and greenhouse gas emissions.