Glossary
W-9
Definition
A W-9 (IRS Form W-9, Request for Taxpayer Identification Number and Certification) is the form a U.S. business asks a vendor or contractor to complete so it can report payments to the IRS.
Why it matters operationally
You generally can't issue a 1099 — or, in many cases, make a payment cleanly — without a current W-9 on file. A missing or stale W-9 can trigger backup withholding and creates audit risk.
Example
A marketing agency you pay $4,000 needs to be issued a 1099, which requires their W-9.