Process planning and scheduling are considered as two separate and distinct phases in manufacturing. Traditional approaches to these problems do not consider the constraints of both domains simultaneously and can only result in sub-optimal solutions. This separation becomes a barrier to further improving manufacturing performance. Most process planning and scheduling systems are off-line and centralized. The process plans generated off-line may become invalid at the time of plan execution. On the other hand, scheduling based on rigid process plans may have already lost the optimal options. Today, there is an increasing need for the integration of process planning and scheduling to generate more realistic and practical solutions. This paper provides a literature review on the integration of process planning and scheduling, particularly on agent-based approaches. It is followed by an overview of our approach toward distributed process planning and scheduling. The paper is finally concluded with future research opportunities.