A purchase order (PO) is a formal document that records an organisation’s authorised commitment to buy specified goods or services from a supplier. It gives the buyer, supplier, procurement and finance teams a shared record of scope, price, quantity, delivery and approval.
TL;DR
A PO is issued before the supplier invoice whenever the process is working as designed.
It helps control commitments, enable invoice matching and create reliable spend data.
A PO is not a substitute for a contract; the two documents serve different purposes.
What is a purchase order?
A purchase order is the transaction document a buyer sends to a supplier after the relevant request, approval and commercial checks are complete. It typically identifies the buyer and supplier, ordered items or services, quantities, pricing, delivery details, payment terms and a unique PO number.
Once accepted, the PO gives both parties a clear reference for fulfilment and billing. Internally, it also records a financial commitment against the appropriate budget, entity, cost centre or project.
How does a purchase order fit into procure-to-pay?
A stakeholder raises a need.
The organisation confirms the right supplier, contract or buying channel.
The request is approved under the relevant policy.
A PO is created and sent to the supplier.
Goods or services are received or accepted.
The invoice is matched to the PO and, where appropriate, the receipt.
The invoice is approved and paid.
Not every purchase needs the same route. The key is to make the appropriate compliant path easier than an off-system workaround.
Purchase order vs invoice vs contract
Document | Primary purpose | Typical timing |
|---|---|---|
Purchase order | Records an approved order and commitment | Before delivery and invoice |
Invoice | Requests payment for delivered goods or services | After delivery or according to agreed billing terms |
Contract | Sets the legal and commercial terms of the supplier relationship | Before or alongside ongoing purchasing |
What a good PO process controls
Authority: the right person approved the commitment.
Budget and coding: the spend has an accountable owner and financial treatment.
Supplier choice: the purchase uses the right supplier, contract or catalogue.
Price and scope: the supplier can fulfil against a clear agreed record.
Invoice matching: finance can identify and resolve exceptions before payment.
Common purchase-order problems
Creating POs after the invoice arrives, which records spend without controlling the commitment.
Using generic descriptions that make the order impossible to verify or analyse.
Sending a PO without confirming the supplier, contract and price are correct.
Forcing low-value routine purchases through the same process as complex strategic buying.
Measuring PO compliance without investigating why users work around the process.
How to improve PO compliance
Start with the user journey. Make it easy to find approved suppliers and buying channels; remove approvals that do not change a decision; keep supplier and catalogue data current; and design a practical route for legitimate exceptions. PO compliance improves when the preferred route helps people do their job, not when it is only enforced after an invoice arrives.
Frequently asked questions
Is a purchase order legally binding?
It can have contractual significance depending on the terms, acceptance and jurisdiction. Procurement teams should use their organisation’s agreed purchasing terms and involve legal counsel where needed.
Can a supplier invoice without a PO?
Yes, but whether the organisation will process and pay it depends on policy and the nature of the purchase. A no-PO invoice should trigger an appropriate review rather than automatically become the normal route.
Does every purchase need a PO?
No. The appropriate approach depends on value, risk, regulatory requirements and buying channel. The policy should be clear about what is exempt and why.
Where do POs live?
They commonly sit in an ERP or procurement platform, which should be clear about the system of record and any workflow hand-offs.
Continue exploring
Read the procure-to-pay guide for the end-to-end process and ERP explained for the system-of-record context.