We are building a next-generation dairy systems simulation model that has the flexibility to represent the diversity of management practices on U.S. dairies and is adaptable to our continually growing knowledge of dairy systems. Our Ruminant Farm Systems (RuFaS) model combines knowledge of management, soils, crops, animal nutrition and husbandry, and weather to predict farm productivity, nutrient cycling and loss, energy and water use, GHG emissions, and production costs. By predicting both production and environmental impact under diverse management and climate conditions, RuFaS provides a platform to assess whole system impacts of management strategies and new technologies under current and future climate conditions.