When goods are purchased on credit you will receive a bill from the seller. Such a bill is called 'Invoice’. It contains the details pertaining to the quantity, description, price, trade discount, total amount, etc. It is generally prepared in duplicate. The original is given to the buyer and the duplicate is retained by the seller. The entries in the Purchase Journal are made on the basis of the purchase invoices received. Although the invoices bear a number but the buyer accords his own serial number to all inward invoices for easy reference. It is this serial number which will be entered in the invoice number column of the Purchases Journal.