Researchers have recognized engineering changes affecting operations as a major obstacle to the delivery of the product in ETO environment. However, there is little academic literature addressing sources of engineering changes that affect materials management throughout the order fulfillment process in an ETO environment. The key research question addressed in this paper is how the substantive sources of engineering changes impact materials in ETO environment can be identified and categorized. Due to the nature of different supply chain configurations different engineering change situations exists within and across these companies.