Purchase Orders (PO)

A purchase order (PO) is a legally binding commercial document issued by a buyer to a seller that formally authorizes the purchase of specific goods or services at agreed-upon terms. Once the seller accepts it, either explicitly or by fulfilling the order, it becomes an enforceable contract that establishes the quantity, price, delivery date, and payment terms.

How purchase orders work

The PO process follows a standard sequence:

1. The buyer creates the PO. The document specifies the required items or services, quantities, agreed-upon prices, and delivery expectations.
2. The PO is sent to the seller. It’s transmitted electronically or in paper form.
3. The seller accepts or rejects the PO. Acceptance converts the PO into a binding contract.
4. Goods or services are delivered. The seller fulfills the order per the agreed terms.
5. The seller issues an invoice. The invoice references the PO number, allowing the buyer to match and verify charges before payment.

The PO number links the original order to the invoice and any subsequent records throughout this process.

Key elements of a purchase order

A standard PO includes:

• PO number. A unique identifier for tracking
• Buyer and seller information. Legal names, addresses, and contact details
• Item description. Clear description of goods or services
• Quantity and unit price. Units ordered and agreed price per unit
• Total amount. Full order value
• Delivery date and location. When and where delivery is expected
• Payment terms. Timeline and method (e.g., net 30, net 60)
• Authorized signature. Buyer confirmation that the order is approved

Vague or incomplete POs are more likely to result in disputes.

Why purchase orders matter

POs create a documented paper trail for every transaction, which supports financial oversight and dispute resolution. For businesses with multiple employees or departments making purchases, they also function as an internal control, as they require approval before spending, which helps prevent unauthorized purchases and budget overruns.

A properly issued and accepted PO constitutes a contract under general contract law. Both parties carry enforceable obligations: The buyer will pay, and the seller will deliver as specified.

Purchase orders vs. invoices

A PO is issued by the buyer before the transaction; it is an offer to purchase. An invoice is issued by the seller after delivery; it is a request for payment. The two documents should align on quantities and prices, and verification is essential. Discrepancies are a common source of payment delays and vendor disputes.

Three-way matching: Verifying that the PO, receiving report, and invoice all agree before releasing payment is one of the most effective controls for catching billing errors and preventing duplicate payments.

When to use a purchase order

Not every transaction requires a formal PO. Small, incidental purchases from trusted vendors may not justify the administrative overhead. Most organizations set a minimum dollar threshold below which purchases can proceed without one, while requiring a PO for larger orders or any transaction where terms could be disputed.

For recurring vendor relationships or large orders, using a PO is advisable. Note that a PO becomes binding only when the seller accepts it; sellers can reject POs or propose modifications, which the buyer must then accept or decline.

Related terms

• Membership interest purchase agreement: A formal agreement governing the sale of ownership interests in an LLC, distinct from a standard commercial PO.
• Compliance in business: How purchase order processes fit into a company's broader regulatory and internal compliance obligations.
• Legal notice: Relevant when a vendor dispute escalates, and formal notification is required.

FAQs about purchase orders

What is the difference between a purchase requisition and a purchase order?

A purchase requisition is an internal document requesting approval for a purchase within an organization. A PO is created only after approval is granted and is then sent externally to the seller as the binding document.

How does a purchase order get paid?

A PO authorizes a purchase but does not trigger payment. Payment occurs after the seller delivers and issues an invoice referencing the PO number; the buyer then verifies the invoice against the PO before releasing funds.

Can a seller modify the terms of a purchase order after receiving it?

A seller can reject a PO or propose different terms, but those modifications are not binding unless the buyer accepts them. If the seller begins fulfilling the order as written, that conduct generally constitutes acceptance of the original terms.