This paper presents a method for assessing the business value of information system scenarios. The purpose of the method is to provide information system decision makers with high quality information about potential future scenarios at a relative low cost of investigation. The method features three frameworks; one for functional assessments of information system scenarios, one for non-functional assessments of information system scenarios and finally a general business value taxonomy. The former two serve as an input structure to the latter one. The business various concepts in the business value taxonomy were prioritised by business managers to reflect the organisation's business needs. A problem with estimating the business value of an information system scenario is that it is a very complex undertaking; there are a vast number of aspects that need to be assessed in order to get a correct result. To be cost efficient all of these aspects cannot be addressed so the results of the method will inevitably contain a degree of uncertainty. The method thus also provides an estimate of the uncertainty of its results. The method has been tested in a comprehensive case study at a large European power company.