The planners job is to ensure that there is sufficient supply of materials and productive capacity to manufacture products within the time demanded by the market place. Where the product range is limited and fixed, the task is clear.  A “Master Schedule” can be set for each end item, which purchasing and manufacturing can respond to through a periodic MRP explosion of demand.  If lead times are long, then there is the option to hold finished goods stocks. Lean Manufacturing introduces the make to order challenge where production lead times are contracted within the lead time offered to the market.  Many companies go further by designing product ranges that can be configured to customer order. Clearly, the old planning techniques can no longer cope.  Orders must be taken, configured, made and shipped in a time that most MRP systems cannot react to.