Using JOINs With Nullable Values

Hi all,

I am using a SQL statement with a JOINs to display a summary list of Work Orders with some information from the related Purchase Order.  I don't require that a Work Order be attached to a Purchase Order, so the JOIN field, POLineItemID, may not be present.  My current problem is that my summary page does not show Work Orders that have a NULL value for POLineItemID -- ie, the JOINing field becomes required.

How can I continue to use this JOIN structure but still return rows that don't have this JOIN field?

Thanks in advance for your help.  Here is my SQL statement for this...

SELECT     tblWorkOrder.WorkOrderNumber, tblWorkOrder.ActualCompletionDate, tblWorkOrder.EstimatedCompletionDate, tblWorkOrder.AssignedTo,
                      tblWorkOrder.DelegatedTo, tblWorkOrder.Due, tblPurchaseOrders.PONumber, tblWorkOrder.POLineItemID, tblPOLineItems.POLineItemID AS Expr1,
                      tblPOLineItems.PurchaseOrderID, tblPurchaseOrders.PurchaseOrderID AS Expr2, tblProducts.ProductID, tblProducts.ProductCategory,
                      tblWorkOrder.ProductID AS Expr3, tblWorkOrder.WorkOrderStatus
FROM         (((tblWorkOrder INNER JOIN
                      tblPOLineItems ON tblWorkOrder.POLineItemID = tblPOLineItems.POLineItemID) INNER JOIN
                      tblPurchaseOrders ON tblPOLineItems.PurchaseOrderID = tblPurchaseOrders.PurchaseOrderID) INNER JOIN
                      tblProducts ON tblWorkOrder.ProductID = tblProducts.ProductID)
ORDER BY tblWorkOrder.Due