The I-539 is a handy form issued by U.S. Citizenship and Immigration Services (USCIS), allowing people in the U.S. on nonimmigrant (temporary) visas to do one of two things, either:
A nonimmigrant visa allows a foreign national to enter and stay in the United States for a specific purpose and a limited amount of time. But what if that time runs out, and you are not ready to leave?
For example, you might be a visitor who is having a great time touring the U.S. and wants to see the Grand Canyon and the Florida Everglades before going home—or you might have had some medical trouble while you were here, necessitating a longer stay.
Or, you might have come to the U.S. on a student visa, and with graduation approaching, found an employer to offer you a job and help you obtain H-1B status.
Or if you're perhaps already here on a work visa, and the project is lasting longer than anticipated such that your employer would like you to stay on, your employer will handle your visa extension for you, but using another form, the I-129 petition.
One important thing to understand about a visa is that it is first and foremost an entry document, issued by a U.S. consulate in another country. While you might think, if your current permitted stay under your visa is running out and you wish to stay longer, "Oh, I'll just stay in the U.S. and apply for a new visa," that's technically impossible. If you literally want another visa, you have to actually leave the United States and visit a consulate, most likely in your home country.
But wouldn't it be easier to just stay in the United States and apply for what you need from there? That's where Form I-539 comes in. It allows you to stay in the United States and ask USCIS to change or extend your status.
Not every nonimmigrant visa holder in the United States can apply for an extension or change of status.
First off, most nonimmigrant visas come with a maximum time its holder can spend in the U.S., allowing at most one or two extensions.
Second, U.S. immigration laws prohibit certain types of changes of status. For example, if you came to the U.S. on the Visa Waiver Program (VWP), you cannot extend or change your status at all. If you came on a B-2 tourist visa, you cannot change to student status (F-1 academic or M-1 vocational) unless you previously got a notation in your visa saying you'd be looking at schools. If you came on a J-1 visa, you might need to comply with a two-year home residency requirement before returning to the United States, or you might need to get a waiver of the home residency requirement.
Research the terms of your particular visa or other visa options carefully before proceeding, or talk to an attorney.
If at all possible, you should file an extension or change with USCIS at least 45 days before the expiration date on your visa. Keep proof of your application with you to show you have followed the proper procedures case your status in the U.S. is questioned by authorities.
See Applying for an Extension of a U.S. Visa or Change of Status for tips on completing the form and other required steps.
If you came to the U.S. on a nonimmigrant visa but have become eligible for a green card—for example, you have married a U.S. citizen or found an employer to sponsor you for a permanent job—Form I-539 will not help you.
With any luck, you will be able to seek "Adjustment of Status," which uses Form I-485 and allows you to complete all of your processing without leaving the United States. Unfortunately, not everyone can use this procedure—some people need to apply for their green card through "consular processing," which requires leaving the U.S. for an interview at a U.S. embassy or consulate in their home country.
Consult an immigration attorney for a full analysis and details on your situation.