Eight models ranging in complexity were compared in a potato modelling case study. Data sets for the comparison case study were provided by the Scottish Crop Research Institute and focused primarily on potential yield, water-constrained and nitrogen-constrained yield. The data sets consisted of information on meteorology, crop development, crop growth, crop yield, details of husbandry, soil water data and soil profile characteristics (physical and chemical). These data sets were sufficiently comprehensive for both the water and nitrogen experiments to allow for performance indication on the wide variety of models used. The data obtained in the first year was used to validate the models, since only limited information was provided and soil water storage, crop development and crop growth results had to be predicted. The main objective of the case study was to present a league of performance indicators for the wide variety of models used in the study by placing special emphasis on the parameterization and calibration procedures used. A modelling comparision case study with a common data set ensures valid comparison and encourages objective discussion about the applicability of the individual models. The modelling groups participating in the case study exchanged information at the First International Potato Modelling Workshop held in Wageningen, The Netherlands, in May 1990. Keynote presentations addressing the physical concepts were discussed and the performance of individual simulation models used in the comparison study was compared. The book is the result of the Workshop and of subsequent thorough analysis of the modelling approaches involved in the case study and extensive feedback from the individual model developers. The text is intended for researchers in the field of simulation modelling and parameterization of plant processes, soil water dynamics, nutrient dynamics and crop growth.