This paper presents an integrated system for assembly planning and redesign, based on 'Design for Assembly (DFA)' principles. DFA criteria are used in the generation of cost effective assembly sequences for mechanical products, using a technique known as 'Backward Assembly Planning'. If the assembly cost can be further reduced by redesign, the system performs 'Reverse Engineering', produces a default design plan, and provides assistance in a DFA-based redesign process. The planner also takes into account special processes encountered in assembly, such as cleaning, painting and testing, in search for an optimum assembly sequence. The paper presents the architecture of the combined system, properties of the planning and redesign modules and their implementations. Also described is how the combined system can provide an effective method of DFA compared to currently available DFA tools. The system is designed to be compatible with either robotic, manual or automated assembly.