This document discusses inventory systems in accounting. It describes the periodic and perpetual inventory systems that small and large organizations use respectively. Under the periodic system, inventory is determined at the end of an accounting period, while under the perpetual system inventory records are continuously updated. The document also outlines different inventory costing methods used under the perpetual system, including FIFO, LIFO, simple average, weighted average, simple moving average and weighted moving average. It emphasizes the importance of inventory in accounting as it helps ascertain profit and loss.