During any strategic development, a ® rm has to position itself in its supply chain. The decision as to how many activities in the chain to occupy is known as vertical integration and is termed as make-or-buy when an individual activity is considered. Because of its very nature, this category of decisions may be made only within the framework of an extended enterprise. To support such a decision-making process, a model is described that de® nes all key elements needed to make such critical decisions. More precisely, a set of rules must present all items which have to be de® ned and valued, and the relationships between them, in order to conclude if an activity must be processed internally (Make) or supplied externally (Buy). This paper details such a hierarchy of rules.