What is a purchase order (PO)?

A PO turns a buying decision into a record: these SKUs, these quantities, these prices, this delivery date, sent to this supplier, approved by this person. Once the supplier accepts it, both sides have the same answer to "what did we agree to," which is the entire point. Phone orders and email threads work fine right up until the invoice doesn't match anyone's memory. A PO also does quiet operational work after it's sent. It represents inbound stock, so the system can show on-order quantity alongside on-hand and stop two people from reordering the same shortage. It gives receiving a checklist to count against. It gives accounts payable the reference for three-way matching. And the PO history per supplier becomes the dataset for measuring actual lead times and price drift. Where teams trip: the threshold problem. Writing a formal PO for every $30 order feels like bureaucracy, so people skip the system entirely, and soon a third of spend has no record. The workable pattern is a fast path: small orders get a lightweight PO created in seconds (or drafted automatically from a reorder suggestion), with approval rules that only add friction above a spend threshold. The discipline that matters isn't ceremony; it's that every order, however small, exists as a record someone can check the delivery against.