Planning production processes for product families (i.e., process family planning) has been recognized as a key to achieving production efficiency. In view of the advantages of Petri nets (PNs) for modeling large systems and the potential of knowledge-based systems (KBSs) for solving complex problems, we develop a methodology integrating PNs and KBSs to support process family planning. An integrated product-process family structure, called IP2S, is proposed to organize data pertaining to a product family and the corresponding process family. Accordingly, a PN model integrating the principles of several well-defined PN extensions is further developed to model the dynamics of process family planning (i.e., how production processes are planned for a product family). Based on the methodology, a prototype is developed, and applied to planning production processes for a truck family.