This research focuses on the development of an object- oriented case-based process planner which combines the advan- tages of the variant and generative approaches to process plan- ning. The case-based process planner operates on general 3D prismatic parts, represented by a collection of features (eg: slots, pockets, holes, etc.). Each feature subplan is developed by the case-based planner. Then the feature subplans are combined into the global process plan for the part via a hierarchical plan merging mechanism. Abstracted feature subplans correspond to cases, which are used in subsequent planning operations to solve new problems. The abstracting and storing of feature subplans as cases is the primary mechanism by which the planner learns from its previous experiences to become more effective and effi- cient. The computer-aided process planner is designed to be ex- tensible and exible through the effective use of object-oriented principles.