Chapter one deals with the general concepts involved in this work, scope and limitations, technique used to solve the problem with mathematical tools. Chapter two defines inventory problems, birth of inventory and various inventory models. Chapter three investigate a two stage partial trade credit policy with deteriorating items, where we determined the optimal cycle time. In chapter four two opportunity of permissible delay in payments with incremental and cash discount scheme are discussed in two sections respectively. Chapter five examines two stage credit policies with imperfect items where the determination of optimal ordering policies for retailer is prepared. Two stages of economic production quantity model with limited storage space are analyzed algebraically in chapter Six. In chapter seven two cases of variation in production corresponding to variation in demand and variation in production with variation in demand are discussed. Chapter eight deal with optimal ordering policies for retailers with different types of demand under progressive payment scheme.