In the first chapter an EOQ model is developed for a deteriorating item with quadratic time dependent demand rate under trade credit. In the second chapter, an economic order quantity model is established for deteriorating items with inflation under the condition of permissible delay in payment. We show that the average cost per unit time is a convex function of cycle time. In the third chapter, we develop inventory model for stock- dependent demand with different holding cost function. In the fourth chapter we derived an inventory model for deteriorating items with partial backlogging under three different situations. We show that the total cost function is convex with cycle time. In the fifth chapter, we considered two levels of trade credit policy using discounted cash flow (DCF) approach.