If you’re launching a U.S. business as a non-resident or helping founders navigate the basics, you’ve likely come across these acronyms. But what exactly is an EIN? How does it differ from an ITIN? Why do you need one, and what might surprise you about their uses? Here’s a developer-focused breakdown:

EIN (Employer Identification Number): Used by businesses for tax filings, hiring, and opening accounts. You get it from the IRS, and it’s tied to your company—think of it as your business’s Social Security Number. ITIN (Individual Taxpayer Identification Number): For individuals who aren’t eligible for a Social Security Number but need to pay U.S. taxes. This isn’t for business entities, but for people (often founders or foreign investors) who must interact with the IRS. Key differences, unexpected edge cases, and practical advice for remote founders wanting to do things "by the book"—happy to answer questions in the thread.