The way of accounting for vertical integration, of this paper is based on the ‘Porterian’ value system and focuses on the relation between the creation and appropriation of value. The essence of a value system is that at each stage in the system value is created and added to the value created at previous stages. We propose that firms which are unable to appropriate the value they create at the stage they currently inhabit, would find it advantageous to integrate vertically towards stages offering a more attractive relation between value appropriation and value creation. This argument will be illustrated here by the case of a large Dutch bank that integrated vertically towards securities trading.@en