What is an ITIN?
The ITIN (Individual Taxpayer Identification Number) is a tax ID number issued by the IRS for people who need to report US taxes but don't qualify for an SSN (Social Security Number) — which is reserved mainly for citizens and residents authorized to work.
It is not a visa, does not grant immigration status, and does not authorize you to work in the US. It's exclusively a number for tax purposes.
What does a foreign investor need it for?
If you buy a property and rent it out, you must report that income to the IRS — and you need an ITIN for that. You also need it to file your tax return if you sell the property and want to recover the excess withheld under FIRPTA.
Some banks and lenders also request it as part of the financing process, although it isn't always a strict requirement for a cash purchase.
How to apply
You apply using IRS Form W-7, generally along with a tax return or documentation justifying the need for the number (for example, in the context of a sale with FIRPTA withholding). It can be processed through an IRS-authorized 'Certifying Acceptance Agent' (CAA), who can verify your passport without you having to mail it in.
The process takes time (weeks, sometimes months during peak season) — so it's worth starting early if you know you'll need it, instead of waiting until the last moment before a sale or filing taxes.