What is Purchase Order?
A purchase order (PO) is a commercial document issued by a buyer to a seller authorizing the purchase of goods or services.
Definition
A purchase order (PO) is a formal commercial document that a buyer prepares and sends to a vendor or service provider to authorize the purchase of specific goods or services. The PO establishes the legal and commercial terms of the transaction: what is being purchased, the quantity, unit price, total cost, payment terms, and expected delivery or completion date. Unlike a verbal agreement or informal email, a PO creates a clear, documented record that both parties have agreed to the transaction terms. Once the seller accepts the PO, it forms a binding contract between buyer and seller.
How a Purchase Order Works
The purchase order process follows a specific sequence. First, the buyer identifies a need — for example, a marketing agency needs 500 branded notebooks for a client event. The buyer then issues a PO to their preferred supplier, detailing the product specifications, quantity, price, and delivery timeline. The supplier reviews the PO and accepts it, either by signing it or sending a confirmation. Goods are then produced or procured and shipped. Upon delivery, the supplier issues an invoice referencing the PO number. The buyer matches the invoice against the original PO before approving payment. This sequence ensures both parties have a clear, agreed-upon record of the transaction at every stage.
Purchase Order vs. Invoice
The key difference between a purchase order and an invoice is who creates them and when. A purchase order is created by the BUYER before the purchase as an authorization. An invoice is created by the SELLER after delivery as a payment demand. In accounting terms, a PO represents a commitment to spend (a liability), while an invoice represents an actual debt owed. For freelancers and small businesses that work with larger corporate clients, receiving a signed PO can be a positive signal — it means the client has gone through their procurement process and budget has been allocated for your services. Many larger organizations cannot process payments without a corresponding PO number on the invoice.
When Freelancers Encounter Purchase Orders
Freelancers and independent contractors typically encounter POs when working with enterprise or government clients. Corporate procurement departments often require POs to authorize spending and to match against budgets. If a corporate client asks you for a PO number before paying, they may simply need you to include their PO number on your invoice so their accounts payable team can process it. Some freelancers ask clients to issue POs even when not strictly required, as it creates an additional layer of documentation and commitment. If a client provides a PO, always reference its number on your subsequent invoice to ensure smooth payment processing.
Key Takeaways
A purchase order is a buyer-issued authorization document, not a payment request. It protects both buyer and seller by establishing clear terms before work begins. Always reference PO numbers on invoices when working with corporate clients. POs are especially important in B2B, enterprise, and government contexts where procurement is formalized.
Sample Purchase Order — Full Example
Here's a complete example of what a purchase order looks like in practice: --- **PURCHASE ORDER** **PO Number:** PO-2024-1142 **Date:** March 10, 2024 **Requested Delivery:** March 25, 2024 **Buyer:** Brightwave Marketing LLC 350 Market Street, Suite 400 San Francisco, CA 94105 Attn: Procurement — Sarah Chen **Vendor:** Elena Design Studio elean@elenadesign.com --- **LINE ITEMS:** | Item | Description | Qty | Unit Price | Total | |------|-------------|-----|------------|-------| | 1 | Brand Identity Package — Logo, colors, typography | 1 | $2,500.00 | $2,500.00 | | 2 | Website Design Mockups (5 pages) | 1 | $1,800.00 | $1,800.00 | | 3 | Brand Guidelines Document | 1 | $700.00 | $700.00 | | | | **Total:** | **$5,000.00** | **Payment Terms:** Net-30 from invoice date **Delivery Terms:** Digital files delivered via shared folder link **Special Instructions:** All source files to be delivered upon final payment **Authorized by:** Sarah Chen, Procurement Manager --- *This is a sample purchase order for illustration purposes. Real POs may also include shipping terms, insurance requirements, and more detailed specifications depending on the industry and purchase type.*
PO vs. Invoice — Detailed Comparison
Understanding the full distinction between a purchase order and an invoice is essential for anyone working in B2B contexts: | Aspect | Purchase Order (PO) | Invoice | |--------|--------------------|--------| | **Created By** | Buyer | Seller | | **Purpose** | Authorize and initiate a purchase | Request payment for delivered goods/services | | **Timing** | BEFORE the purchase | AFTER delivery | | **Legal Effect** | Buyer commits to buy; seller commits to sell at agreed terms | Triggers payment obligation | | **Accounting Entry** | Creates a "commitment to spend" (budget encumbrance in some systems) | Creates an accounts payable (AP) liability | | **Required by** | Procurement / purchasing departments | Finance / accounts payable departments | | **Contains** | What to buy, quantity, price, delivery date, terms | What was delivered, amount due, due date, payment instructions | | **Can Exist Without the Other?** | Yes — a PO can exist without a corresponding invoice if the order is cancelled before delivery | No — an invoice should reference a PO (or equivalent) if one was issued | **For freelancers:** If a client sends you a PO, it's a positive signal — they've gone through their internal process to authorize spending with you. Always reference the PO number on your invoice to ensure it gets routed to the right person in their AP department. *Source: The U.S. Small Business Administration (SBA) provides* [guidance on purchase orders and procurement documentation](https://www.sba.gov) *for small businesses working with government and enterprise clients.*
Related Glossary Terms
Continue building your understanding of B2B payment and procurement vocabulary: • **[Accounts Payable](/glossary/accounts-payable)** — The department (and accounting function) responsible for paying supplier invoices. When you receive a PO from a client and then invoice them, their accounts payable team will process your invoice using the PO as supporting documentation. • **[Statement of Work](/glossary/statement-of-work)** — A document that defines the specific scope, deliverables, and timeline for a project. Often used alongside (or in place of) a PO to establish project terms before work begins. • **[Net-30 Payment Terms](/glossary/net-30)** — The standard payment term that typically appears on purchase orders. Net-30 means the buyer will pay within 30 days of the invoice date. Always check the PO for the specific payment terms agreed upon.