In the context of sustainable and green chemistry, the ‘benign by design’ concept requires information on a compound's biodegradability to be available at an early stage, even before synthesis. Computer models for predicting biodegradation therefore are increasingly important. In this work various approaches to predict aquatic aerobic biodegradation are critically reviewed from a user's point of view. Some fundamental problems in modeling biodegradation are discussed, as well as more general issues in modeling of compound properties by quantitative structure–property/activity relationships (QSPR/QSAR).