What a W-9 is for
Form W-9 is used to request the taxpayer identification number of a U.S. person, including a U.S. resident alien, together with certifications and tax-classification information. Businesses commonly collect W-9s from U.S. independent contractors and vendors when payments may need to be reported on an information return.
Collect it during onboarding
A W-9 is easiest to obtain before the first payment, when the vendor has an incentive to complete onboarding. Store the form securely because it contains sensitive taxpayer identification information. Do not copy the TIN into casual notes, email subjects, or shared spreadsheets that do not need it.
Do not edit the vendor's tax classification yourself
The payee certifies its own information. If the business name on the invoice differs from the name on the W-9, use the W-9 and current IRS instructions to determine what information belongs on the information return rather than guessing from branding.
U.S. and foreign payees use different documentation
Form W-9 is for U.S. persons. A foreign payee generally provides an appropriate Form W-8 series form instead. Vendor onboarding should therefore ask the status question first rather than sending Form W-9 to every payee in the world.
Retention
The IRS independent-contractor guidance recommends keeping the contractor's W-9 in your files for four years for future reference. Tie the stored form to the vendor record so it can be retrieved during 1099 preparation without exposing the TIN more broadly than necessary.
Use the W-9 as an onboarding record, not a year-end chase
Request the form before or near the start of a U.S. vendor relationship when possible. Review the legal name, business name, federal tax classification, address, and taxpayer identification number for completeness, then store the form securely with restricted access.
Do not overwrite an older W-9 without preserving when the replacement became effective. A vendor can change name, address, entity type, or tax classification, and the company may need to understand which information applied to payments made in an earlier period.
At year-end, compare the vendor master and payment ledger with the W-9 file. Missing or inconsistent information is easier to resolve when the source form and payment history are already organized.