A unique identification number is a distinct code assigned to a person, business, or organization so that government agencies and financial systems can tell one record apart from every other. The Social Security Number is the one most people know, but the federal government issues several others for tax filing, healthcare billing, financial regulation, and government contracting. Each has its own purpose, its own application, and its own upkeep rules.
Social Security Number
The Social Security Number is a nine-digit identifier assigned by the Social Security Administration. Federal law directs the SSA to assign these numbers to citizens, permanent residents, and noncitizens authorized to work in the United States.1Office of the Law Revision Counsel. 42 USC 405 – Evidence, Procedure, and Certification for Payments Most people get one at birth through the hospital, but adults who never received a number can apply directly.
Your SSN tracks lifetime earnings, determines eligibility for Social Security benefits, and identifies you on federal income tax returns. Credit bureaus use it to build your credit history, which is why it’s the single most sensitive number most people carry. Programs like SNAP rely on it to verify eligibility and prevent duplicate enrollment.2eCFR. 7 CFR 273.6 – Social Security Numbers
To apply for an original or replacement card, submit Form SS-5 along with documents proving identity, age, and citizenship or immigration status. Acceptable proof of citizenship includes a U.S. birth certificate or U.S. passport; identity documents include a state driver’s license or U.S. passport.3Social Security Administration. Learn What Documents You Will Need to Get a Social Security Card Applying is free, whether it’s your first card, a replacement, or a correction.4Social Security Administration. Application for Social Security Card (Form SS-5)
Employer Identification Number
The Employer Identification Number is a nine-digit code the IRS assigns to businesses, nonprofits, estates, trusts, and certain other entities for tax reporting.5Internal Revenue Service. About Form SS-4, Application for Employer Identification Number (EIN) You need one if your business has employees, operates as a partnership or corporation, or files employment or excise tax returns.6Internal Revenue Service. Employer Identification Number Banks also require an EIN before opening a business account.
Getting an EIN is free. The IRS online tool issues the number immediately after you finish the application.7Internal Revenue Service. Get an Employer Identification Number You can also apply by fax or mail using Form SS-4. International applicants without a U.S. address can apply by phone.
Form SS-4 asks for the entity’s legal name, physical address, name and taxpayer identification number of the responsible party, the type of entity, the date the business started, and the closing month of its accounting year.8Internal Revenue Service. Instructions for Form SS-4 (Rev. December 2025) Every field needs to match your official formation documents exactly. The form requires a signature from a principal officer or authorized individual.
Individual Taxpayer Identification Number
If you have a federal tax obligation but aren’t eligible for an SSN, the IRS issues an Individual Taxpayer Identification Number instead. The ITIN is a nine-digit number formatted like an SSN, and it exists solely for tax filing.9Internal Revenue Service. Individual Taxpayer Identification Number (ITIN) Anyone who qualifies for an SSN does not need one.
Common situations that require an ITIN include nonresident aliens filing a U.S. tax return or claiming a tax treaty benefit, resident aliens who can’t get an SSN, and dependents or spouses of U.S. citizens or resident aliens who need to appear on a tax return.9Internal Revenue Service. Individual Taxpayer Identification Number (ITIN)
You apply by submitting Form W-7 together with a federal tax return and documents proving your identity and foreign status. A valid passport is the only document that can establish both on its own; without one, you’ll need a combination like a national identification card, birth certificate, or foreign driver’s license. You must submit originals or certified copies from the issuing agency, and the IRS returns them within about 60 days.10Internal Revenue Service. Instructions for Form W-7 (Rev. December 2024)
One detail that catches people off guard: an ITIN expires if you don’t use it on a federal tax return for three consecutive years.11Internal Revenue Service. How to Renew an ITIN If yours lapses, you renew by filing a new Form W-7, but your return processing will be delayed until the renewal goes through.
Legal Entity Identifier
The Legal Entity Identifier is a 20-character alphanumeric code built on the ISO 17442 standard. It uniquely identifies any legally distinct entity that participates in financial transactions, giving regulators worldwide a consistent way to track who is on each side of a trade.12Office of Financial Research. Frequently Asked Questions – Section: How Does the LEI Work? If your organization trades derivatives, issues securities, or falls under reporting requirements in major financial jurisdictions, you likely need one.
Unlike government-issued identifiers, the LEI comes from private registration agents accredited by the Global Legal Entity Identifier Foundation. Fees vary by provider, and annual renewals typically cost under $100 through competitive agents. The LEI Regulatory Oversight Committee requires every LEI to be re-validated at least once a year, and the entity itself must confirm the reference data is still accurate.13GLEIF Blog – News and Media. Data Quality and Risk Management – The Importance of Timely Renewal of Legal Entity Identifiers Miss the renewal deadline and the grace period after it, and your LEI status is set to “lapsed,” which can block you from executing regulated transactions.
National Provider Identifier
The National Provider Identifier is a 10-digit number assigned to healthcare providers under HIPAA’s administrative simplification rules. Doctors, hospitals, pharmacies, and other covered providers use it on every insurance claim, billing transaction, and coordination-of-benefits exchange.14Centers for Medicare and Medicaid Services (CMS). National Provider Identifier Standard (NPI) You apply through the National Plan and Provider Enumeration System, which requires an Identity and Access Management account before you submit the application.15NPPES. NPPES The NPI does not expire, though providers must update their NPPES records when practice information changes.
Unique Entity ID for Federal Awards
Any organization that wants to bid on federal contracts or apply for federal grants needs a Unique Entity ID, generated through SAM.gov. The UEI replaced the former DUNS Number and is now the sole identifier across all federal award systems, including contract databases, sub-award reporting, and contractor performance records.16GSA (U.S. General Services Administration). Unique Entity ID Is Here Registration and UEI assignment are free.17SAM.gov. Get Started with Registration and the Unique Entity ID If you only need the identifier for sub-award reporting rather than bidding directly, SAM.gov lets you request a UEI without completing the full registration.
Keeping Your Information Current
Getting the number is only the first step. Every identifier comes with ongoing obligations, and the consequences of letting things slip range from processing delays to losing the ability to transact.
For EINs, any change to your business’s responsible party must be reported to the IRS within 60 days using Form 8822-B.18Internal Revenue Service. About Form 8822-B, Change of Address or Responsible Party – Business The same form covers changes to your business mailing address or location. Failing to report a responsible party change can create complications when the IRS needs to verify who controls the entity, especially during audits.
LEIs require annual renewal with the issuing organization. ITINs expire after three consecutive years of non-use. SAM.gov registrations need periodic updates too; you make changes to your legal business name and physical address directly through the SAM.gov portal.16GSA (U.S. General Services Administration). Unique Entity ID Is Here The pattern across all these systems is the same: the agency assumes your data is current unless you tell them otherwise, and the burden falls on you.
Protecting Your Identification Numbers
Your SSN and EIN are high-value targets for identity thieves. The IRS classifies both as personally identifiable information that should be stored securely, shared only when you initiate the contact or are certain who is asking, and never routinely carried in a wallet or purse.19Internal Revenue Service. Identity Protection Tips
If your SSN is compromised, the federal IdentityTheft.gov portal walks you through a structured recovery process. The most important immediate steps are placing a free fraud alert with one of the three credit bureaus (which then notifies the other two) and freezing your credit to block new accounts from being opened in your name.20IdentityTheft.gov. What To Do if Your Information Was Lost or Stolen, or Part of a Data Breach You can also lock your SSN for employment verification through E-Verify’s self-service tool, which prevents someone from using your number to pass a new-hire check.
For tax filing specifically, the IRS offers an Identity Protection PIN that you can request through your IRS online account. The IP PIN is a six-digit number that must accompany your return before the IRS will process it, effectively blocking anyone who has your SSN but not your PIN from filing a fraudulent return in your name.21Internal Revenue Service. Get an Identity Protection PIN (IP PIN) The IRS will never call, email, or text you asking for your IP PIN.
Watch Out for Paid Application Sites
The IRS issues EINs for free, and SAM.gov assigns UEIs for free, yet a cottage industry of lookalike websites charges people hundreds of dollars for what amounts to filling out the same form. The FTC has formally warned operators of these sites that using IRS-like branding, putting “IRS” in their domain names, or failing to disclose that their fees are entirely service charges for a free government product may violate the FTC Act.22Federal Trade Commission. Don’t Pay to Get Your Employer Identification Number (EIN)
The simplest way to protect yourself: always go directly to the agency’s official site. For an EIN, that’s irs.gov. For a UEI, it’s SAM.gov. For a Social Security card, it’s ssa.gov. If a site charges a fee for something the government provides at no cost, close the tab.
Penalties for Providing False Information
Submitting false information on a federal identification application is not just an administrative problem. Under federal law, anyone who knowingly makes a false statement on a document signed under penalty of perjury in connection with the internal revenue laws faces a felony charge. Conviction carries a fine of up to $100,000 for individuals ($500,000 for corporations) and up to three years in prison.23Office of the Law Revision Counsel. 26 USC 7206 – Fraud and False Statements Form SS-4, Form W-7, and Form SS-5 all contain perjury declarations. Make sure every field matches your official documents exactly, and never apply for an identifier using someone else’s information.