Technical Abstract: The Integrated Farm System Model (IFSM) is a process level simulation of the performance of crop, beef and dairy farming systems that estimates major environmental impacts, production costs, and farm profitability. The IFSM simulates all major farm components on a process level. This enables the integration of components in a manner that represents the major interactions among the many biological and physical processes on the farm. The IFSM provides a robust research and teaching tool for exploring the whole farm impact of changes in management and technology. Crop production, feed use, and the return of manure nutrients back to the land are simulated on a daily time step over many years of weather. Nutrient flows through the farm are tracked to predict potential nutrient accumulation in the soil and loss to the environment. Environmental impacts include erosion of sediment, soluble and sediment-bound phosphorus runoff, nitrate leaching, ammonia and hydrogen sulfide volatile loss, all greenhouse gas emissions, and the farm gate water, reactive nitrogen, energy, and carbon footprints of the production system. Simulated farm performance is used to determine production costs, incomes, and economic return for each year of weather. A whole-farm budget is used where annual fixed costs for equipment and structures are summed with predicted annual expenditures for labor, fuel, and other resources to obtain a total production cost. Production costs are subtracted from the income received for milk, animal, and crop sales to determine a net return to management. IFSM was primarily developed for use in the temperate climate regions of the United States, but with suitable climate data and appropriate assumptions, it has been adapted to other regions of the world. Although the model contains many options for crop, feed, animal, and manure management, these options are limited to the major strategies used in the United States. The software and further information can be obtained at http://www.ars.usda.gov/Main/docs.htm?docid=8519. The software is easily installed and used on computers using a Windows® operating system.