Glossary
What is a UEI?
A Unique Entity ID is the number SAM.gov assigns to your entity. It replaced the DUNS number for federal awards. You get it by registering in SAM.gov, not by paying a private reseller.
The UEI is twelve characters. It identifies the legal entity. It is not a certification that you are a small business, and it is not a contract.
How you get one
Start an entity registration at SAM.gov. The record asks for legal name, address, and the people allowed to act for the company. When the registration is active, the UEI is on the record.
How long that takes varies. The status on SAM.gov is the status. Do not plan a proposal deadline around a fixed number of days, and do not pay a third party who promises a faster official UEI. The government does not sell a faster line through a random website.
What to do with it
You will type it on representations, teaming documents, and invoices. Keep the legal name identical to the SAM.gov record. A mismatch is a common reason a package gets questioned.
The CAGE code is a different identifier, issued for the registration. See CAGE code. Both usually show up together once the federal record is active.
This is general information, not legal or tax advice about which entity should hold the registration.