Discusses the basic inventory systems for controlling inventories under uncertain demand and lead-time. The continuous review system and periodic review system are discussed, and determination of control parameters for the two systems is explained. The concepts of service level, safety stock and reorder point are discussed, and formulas for determining safety stock and reorder point for a given service level and order quantity and review interval are provided. The results suggested determining control parameters are approximate and not optimal. Advantages and disadvantages of the two control systems are considered.