Purchase Order (PO)

What Is a Purchase Order?

A purchase order (PO) is a formal document issued by a buyer to a seller authorizing the purchase of specified goods or services under stated terms. It usually includes the buyer and seller names, PO number, item description, quantity, price, delivery instructions, payment terms, tax information, approval details, and any contract or quote reference.

A PO is a procurement control tool. It tells the seller what the buyer is authorizing, and it gives the buyer an internal record for approval, receiving, invoice matching, budgeting, and audit. In many organizations, vendors are told not to start work or ship goods until a valid PO is issued.

How a PO Works

The process often starts with a purchase requisition or approved request inside the buyer’s organization. Once approved, the buyer issues a PO to the vendor. The vendor fulfills the order, the buyer receives goods or confirms services, and the vendor sends an invoice. Accounts payable then matches the invoice against the PO and receiving record before payment.

This is commonly called three-way matching: PO, receiving document, and invoice. The goal is to prevent paying for unauthorized, incorrect, duplicate, or undelivered purchases.

PO Versus Invoice

A purchase order comes from the buyer and authorizes the purchase. An invoice comes from the seller and requests payment. The PO says, “This is what we agree to buy.” The invoice says, “This is what you owe for what we provided.” Confusing the two can create payment delays and accounting errors.

A quote is different again. A quote is usually the seller’s proposed price or scope. The PO is the buyer’s authorization based on that quote, contract, or negotiation. A receipt confirms delivery or performance.

Business Controls

POs help businesses enforce spending authority. A department manager may be allowed to approve purchases up to a threshold, while larger purchases require finance or executive approval. The PO creates an audit trail showing who approved what, when, and under which budget.

POs also help vendors. A clear PO reduces disputes about scope, quantity, shipping, taxes, billing address, and payment terms. For small businesses selling to larger customers, obtaining a PO number can be the difference between smooth payment and an invoice stuck in procurement.

Example

A company needs 50 laptops. Procurement issues a PO listing the model, quantity, unit price, delivery location, and payment terms. When the laptops arrive, receiving confirms quantity and condition. The vendor invoices against the PO. Accounts payable pays only if the PO, receipt, and invoice match within allowed tolerances.

A PO also helps with budgeting because it records a commitment before cash leaves the business. Finance teams can see approved spend, open commitments, received-but-not-invoiced goods, and invoices awaiting match. That visibility matters for cash planning.

For sellers, the PO number is often essential to getting paid. Large customers may reject invoices that lack a valid PO number, even if the work was performed. Small businesses should confirm PO requirements before starting work for procurement-heavy customers.

Clear PO discipline turns purchasing from informal spending into controlled commitments.

The Bottom Line

A purchase order is a buyer-side authorization and control document. It matters because it connects procurement approval, vendor fulfillment, receiving, invoicing, and payment into one auditable workflow.