The Dairy Forage System Model, DAFOSYM, is a simulation model of the dairy forage system created by Engineers and Scientists of the U.S. Dairy Forage Research Center and other cooperating institutions. This model simulates the production, harvest and feeding of crops, the production and handling of manure, and the costs and returns of user described, representative dairy farms. A farm is simulated over many years of weather for a selected location. The model is most useful for evaluating and comparing the long term performance and costs of alternative technologies and management strategies for the dairy farm. Although the model was primarily created and used as a research tool, we feel it can provide an effective teaching tool for illustrating the effects and interactions that occur when changes are made to the dairy farm.