Product definition creation and management are critical aspects of the new product development process. A well-developed product definition reflects understanding of customer and user needs, the competitive environment, technology availability, and regulatory and standards issues. A robust product definition is one that stands up to challenge and guides the product development process, allowing the development team to make tradeoffs and decisions quickly and effectively. This article examines the product definition creation and management processes at six major U.S. electronics companies. Customer and user needs assessment is a particularly critical aspect of product definition; clear, widespread communication of product definition elements throughout a product development team is important; and change to a product definition during product development must be carefully and explicitly managed to obtain the best chances of overall product success. Many of the firms in this study used surprisingly rudimentary procedures to bring together the requisite product definition information and failed to distinguish the creation of product definition as an important phase of the product development process. Further, few of the firms understood that product definitions will change during product development and they did not have mechanisms for managing that change.