This chapter introduces Enterprise Resource Planning (ERP) and its antecedent, material requirements planning (MRP). First, it discusses the evolution of ERP, its goals, modules, and costs. Examples of use and important vendors are then discussed. The chapter then describes MRP. The difference between independent and dependent demand is presented. It presents an overview of its objectives, the necessary inputs to MRP and its operating logic. Various lot sizing rules are presented and compared. Capacity requirements planning is described and demonstrated.