in my Query i have 4 fields, Number - Description - Customer - Date.
the data all comes from one table but i only want the form to show data from the "Number" field when the "Date" field is blank.
Can someone please give me the criteria statement to do this please.
I would like to show the results in text boxes (1 for each) when the user selects a customer and a product from combo boxes, so the query will run in the afterupdate event of the second combo box

Do you only want records in which the date field is blank? Is Null in the criteria for that section in your query will work.
I don't think that's what you're asking though. Look at using the iif statement.
I.e. Control source = IIf(IsNull([DateField]),[NumberField],"")

However this will make that field calculated and therefore non-updateable from your form.