The main objective of this book is to find the inventory parameters at the optimum state. Inventory parameters in the deterministic or stochastic state are on the timing of order cycle, the inventory order up to level and safety stocks for each item. It is required to model the inventory system in continuous and discrete time frames, then constructing user friendly software that could accept different items with different attributes sharing a major order cost and minor order cost for each item. Furthermore, this system is to be applied in a multi- echelon system. In order to achieve these goals, a deterministic model is constructed to deal with multiple items, with continuous and discrete demands. Stochastic inventory policies for continuous demand are modeled under different conditions. A proposed policy is suggested for the JRP with stochastic demand, a new method is applied on the traditional (T,S) policy to gain more control and hence to reduce the order up to level S. This method is applied for multiple items, multiple locations, to reduce the amount of safety stock required at each location.