Traditionally, process planning and scheduling were performed sequentially, where scheduling was executed after process plans had been generated. Considering the fact that the two functions are usually complementary, it is necessary to integrate them more tightly so that the performance of a manufacturing system can be improved greatly. In this chapter, a multi-agent-based framework has been developed to facilitate the integration of the two functions. In the framework, the two functions are carried out simultaneously, and an optimisation agent based on evolutionary algorithms is used to manage the interactions and communications between agents to enable proper decisions to be made. To verify the feasibility and performance of the proposed approach, experimental studies conducted to compare this approach and some previous works are presented. The experimental results show the proposed approach has achieved significant improvement.