It has long been accepted that a realistic view of what happens between customer companies and their suppliers cannot be achieved by examining single purchases alone. Instead, a single purchase can only be understood as part of a supplier-customer relationship which both affects and is affected by it. Also in business markets, a customer's purchase behaviour is not simply a passive response to the marketing actions of a supplier, but part of the interaction between an active customer and supplier. A major element in this interaction is likely to arise from the efforts of the customer to develop its own products interactively with a network of suppliers. This paper reports on a study into the ways in which customers employ the skills of their network of suppliers and attempt to direct that network in product development projects. The paper suggests that customers are likely to use either of two alternative strategies for product development, that we term "network delegation" and "network intervention". The paper draws on four in-depth case studies to highlight the types of situation where customers are most likely to employ each of these strategies and draws conclusions for marketers about the implications of each approach.