Product/service family engineering, which encourages the development of a common product platform, plays a key role in facilitating large-scale and planned reuse in the development of customized products. In product family designs, managing points of variability is critical to achieve product variety. Variation points are points at which one among the several possible variations of a feature of a system can be selected to achieve different configurations of a product. We are developing an ontology that catalogues the different concepts associated with variability. This ontology is used to define the elements characterizing the knowledge elements necessary for managing variability in product/service families. We have also developed a knowledge management system integrated with an ontology development tool to facilitate knowledge capture and retrieval for variability management.