If you are a U.S. citizen or lawful permanent resident, and you have a friend or relative who seeks to come to the U.S. as a tourist (on a B-2 visitor visa), you might be able to help the person by providing a letter of invitation. It's not a requirement, but it can help smooth the way.
Getting a U.S. tourist visa can be challenging, because the U.S. government is worried about the number of people who use these as a way to enter the U.S. and then never leave, or who overstay by days, months, or years.
The aim of your letter would be to show the U.S. consular officer who considers the visa application that the person has a specific plan regarding visiting (and eventually leaving) the U.S., perhaps has a place to stay, and will not need to find work in order to support him- or herself while here (if, that is, you plan to offer financial backup or support).
This should be a personal document, not something like a lawyer would write, so don't stress over making it sound official. Make sure to include both your and the recipient's name and full address, for example using the format shown below.
Also be sure to cover:
Be as specific and detailed as possible. Below is a sample letter for you to use as a guide.
You can give this letter to your friend or relative to take along to the U.S. consulate when her or she presents the application for a U.S. visitors' visa.
If you plan to provide financial support to the visitor while he or she is in the U.S., and don't feel like writing a letter, you can fill out USCIS Form I-134, called an Affidavit of Support. Or, you can provide both a letter and a Form I-134.