This thesis deals with the development and the first empirical examination of an assessment method and decision support tool for the ex ante assessment of margin to be applied in ICT-enabled redesign of business networks.  Many industries face the demand for customisation. This customisation challenges them to tailor products and services to the specific requirements of every individual customer, while at the same time maintaining their current levels of economies of scale. It forces organisations to become more flexible (defined in terms of their ability to produce different and customised products) towards the market without losing profitability, i.e. margin. Managers start to question the suitability of their current organisational design, which originates from the traditional supply chain and become increasingly aware of the benefits of a different approach to organisational design: ICT-enabled business networks, to respond quickly to a changing environment. However, managers struggle with how they should accomplish this, and to what extent it will influence their current level of flexibility and profitability. Therefore, they need a method and managerial tool that can help them assessing the reengineering of a business network - in particular, prior to performing the actual change in the business network.  For this purpose, the described assessment method and decision support tool, called Business Network Navigator, was developed