ALSIM 1 (Level 1) is a dynamic computer simulation model of alfalfa (Medicago sativa L.) growth and management written in CSMP. Condition of the crop at the start of simulation, dates of cutting, and solar radiation and average air temperature data are needed as input. The model predicts yield of hay and growth curves for leaves, stems, basal buds, and total nonstructural carbohydrates of the taproots (TNC) with time steps of one day. Following a simulated harvest, the model overestimates top growth and underestimates TNC levels, apparently because of insufficient understanding of the regrowth processes. The most significant contribution of the model is the identification of the importance of and need for research in the area of regrowth physiology. A discussion of model performance, instructions on how to use the model, and examples of simulation runs are included in the report.