What Is a Purchase Order?

A purchase order (PO) is a document a buyer sends a supplier to authorize a purchase. It lists what is being bought, the quantity, the agreed price, the delivery date and a PO number. Once the supplier accepts it, it sets the terms of the deal.

Freelancers and small businesses run into POs when they work with larger companies. Many corporate accounts teams won't pay an invoice unless it quotes a valid PO number, because their system matches each invoice against the PO and the delivery record before releasing payment.

The usual flow is: you send a quote, the client approves it internally and raises a PO, you do the work, and your invoice quotes the PO number. The buyer issues the PO and the seller issues the invoice. If the invoice amount doesn't match the PO, expect a delay while someone approves the difference.

Ask for the PO number before you start, and put it near the invoice number, where the client's accounts team will look for it.