Production management is concerned with the efficient transformation of inputs into desired outputs. Usually the operations are carried out under conditions of uncertain and fluctuating customers’ demand, varying procurement lead times for difference inputs, and the necessity to fix the production schedules long before the magnitude and the mix of the orders that must be filled from the resulting output can be determined. Under certain conditions it is possible to view production of this kind as a closed, self-regulating system which may be studied using some common techniques and procedures.