A purchase order (PO) is a commercial document and first official offer issued by a buyer to a seller indicating types, quantities, and agreed prices for products or services. It is used to control the purchasing of products and services from external suppliers. Purchase orders can be an essential part of enterprise resource planning system orders.
The issue of a purchase order does not itself form a contract. If no prior contract exists, then it is the acceptance of the order by the seller that forms a contract between the buyer and seller.