Factors that complicate bioenergy model building are presented and discussed. Important aspects of ＇real-life＇ energy systems that are difficult to represent in modelling are: the cost structure of energy production, information asymmetry, socioeconomic factors, household economics, strategic considerations, and policy uncertainties. The modeller can employ different strategies in dealing with these problems. Complicating aspects can be quantified and integrated in the model, mentioned when the implications of the model are discussed or they may merit separate quantitative or qualitative investigations. The authors make some recommendations as to how these aspects could be considered in the modelling work to improve model accuracy. (C) 2000 Elsevier Science Ltd. All rights reserved.