Spin-off companies are generally considered a promising vehicle for developing academic knowledge into products that are ready for the market. In this paper the authors explore under what circumstances spin-off companies can serve as a source of knowledge for the research organization from which they originate. The paper brings together literature from different academic fields to construct an analytical framework for investigating knowledge feedback mechanisms between spin-off companies and their parent research organizations. The authors illustrate the application of this framework in six case studies of parent-spin-off couples in the water technology sector. These case studies show that the interaction with spin-off companies can yield important cognitive benefits for the academic research process, such as an improvement of the research agenda and new insights about the practical operation of theoretical models and technologies. These benefits were facilitated mainly by staff exchange, collaborative research and personal contacts.