I think you've misunderstood what VLOOKUP does—either that or your function contains a simple typo. What you want is You're starting with the value in VendorInventory!$A2, you see, and looking that up in InventoryOnHand; so the first argument in the VLOOKUP call must be the value on this sheet that you want to look up on the other sheet.

And by the way, I think it'll be simpler and work just as well to do it this way:That way you don't have to update the formula on the first sheet whenever you add new inventory items to the second.