Lot sizing is a decision made in productive systems operation, where a batch size or order quantity is selected critically to optimise the process in terms of specified characteristics and such that costs are minimised and demand requirements meet. The optimal decision is the Economic Lot Size (ELS) or the Economic Order Quantity (EOQ). For now a productive system (manufacturing system) will be broadly defined as the value adding process of transforming raw materials or work-in-progress (WIP) components into saleable finished goods (FG).Managers and engineers are required to make such decisions throughout the manufacturing industry, wherever batches are produced. From global refrigerator and whitegoods producer, Fisher and Paykel, where each output unit is comprised of hundreds of individual components, to local surfboard blank producer, Southern Foam and Plastics Pty Ltd, whose outputs only contains one component, economic lot sizing is of vital importance to efficient production.Lot sizing issues need to be addressed in many various stages of a manufacturing process and the accurate determination of an economic value is vital to the efficiency of the production and operations systems.From a process supply perspective, a productive systems manager or engineer will need to make important lot-sizing decisions considering several key quantitative and qualitative factors. This can be considered inventory management and primarily the decisions regard the ordering of input resources to supply the process system, and aim to meet process demand while minimising costs, such as inventory holding costs. ....................