The purchase order or also called "order order" or "purchase order",[1]​ is a document by which the seller and the consumer express their agreement on the order and its price; especially in cases where the purchased object cannot be delivered immediately. If a good or service cannot be delivered immediately, the buyer and seller can reflect in writing the terms of the operation and its price through a purchase order.

From the moment this commercial document is signed, the sale is considered to exist. The order form is only mandatory when a payment is made on account. Consequently, said document should not be confused with a price quote, where in that case, only information about the values ​​of a product or service is required, without the obligation to purchase it.[2]​.

In addition to establishing an agreement between buyer and seller on the terms of the transaction, the purchase order offers legal security for both parties, protecting in cases of non-compliance such as non-payment or non-delivery of the agreed goods. It also optimizes business management by facilitating more agile control of inventory and finances. In particular, electronic purchase orders improve process efficiency, allowing buyers to check stock and delivery times online. [3]​.

Order forms usually contain the following data:

Two copies of the order form are usually issued, one for the buyer and one for the seller. The original document is for the seller and implies that he must prepare the order, while the duplicate is for the buyer as proof of the goods or services requested.

This improves clarity on payment and delivery terms, as well as ensuring good communication between both parties.