Product Service Systems (PSS) are new industrial offerings which integrate a product and related services into a customer-specific bundle and offer the customer an overall solution to a specific issue. The lifecycle of PSS is characterized by merged product and service structures and a close interaction among the provider, the suppliers, and the customer, not only in the development phase but especially during the operation of PSS. Therefore a lifecycle management approach for PSS has to merge both the virtual and real (operational) lifecycle of PSS. To reach that goal operational knowledge about a PSS instance must be gathered, aggregated, managed, and used by enhanced lifecycle management methods in order to support providers, suppliers, and customers by developing, delivering and operating PSS. The paper in hand presents a knowledge-based lifecycle management approach for PSS, which considers an ontological representation of PSS knowledge and 3 knowledge-based lifecycle methods to make engineering processes adaptive, to provide the involved actors with the appropriate PSS knowledge and support the stakeholders in their decision making processes. The components of this approach have been identified as key lifecycle management methods for managing PSS. They are still being developed within the collaborative research center TR29 funded by the German Research Foundation (DFG), who investigate the overall engineering of PSS.