The development of product innovations is permanently challenged by the customers' rapidly evolving demand for new products and technologies. New approaches for integrating customers into the product innovation process are required and have been exemplified in a software engineering context by Extreme Programming. Patricia Sandmeier demonstrates how a transfer of elements from Extreme Programming to the development practice of industrial products can improve customer integration activities and the innovativeness of the resulting new products. Based on an in-depth case study analysis of two industrial firms and two technical service firms she presents a conceptual model for the integration of customer contributions into the product innovation process. Finally, the author proposes a product innovation process based on discrete product development steps as well as a 'customer-centered innovation cell' enabling the development of truly innovative product solutions together with customers.