Inventory is a stock of items kept by an organization to meet internal and external customer demand. Inventory is the subject of interest of inventory management. The main objective of inventory management has been to keep enough inventory to meet customer demand and also be cost-effective. The paper reviews the oldest inventory model introduced by F. W. Harris. Harris´s formula, computing EOQ and discussed here, is usually a part of decision support systems or advanced planning modules of an enterprise resource planning. Inventory plays a key role in the logistics behavior of manufacturing systems, but inventory modeling is a very poor field of enterprise practices.