Visa vs Status: What's the Difference?
A visa is a permit to apply for entry into the United States for some specific purpose: study, business, tourism, employment, etc. It is placed in your passport by an official at a U.S. Consulate outside the United States after your application for that type of visa is approved. United States Embassies and Consulates are part of the Department of State.
Unless your country is a participant in the Visa Waiver program, you must have a valid (unexpired) visa in order to enter the United States. However, having one is not an absolute guarantee that you will be permitted to enter; the immigration official who inspects you at the port of entry has the right to reject you. In practice, though, refusal is a rare event and happens only when issues of fraud or security arise. Immigration regulations and officials belong to the Department of Homeland Security.
A visa is like the key to a house. Once you use the key and enter the house, it does not matter if you misplace the key; you are already in the house, and you no longer need the key. Likewise, once you enter the U.S. with your visa, it does not matter if the visa expires; you do not need this visa or any other visa as long as you stay inside the United States.
Once you use your visa and enter the United States, you have a legal non-immigrant status which matches the visa you used. If you use a B2 tourist visa, you have B2 tourist status. If you use an F1 student visa, you have F1 student status, etc.
How long your status lasts depends on what the immigration officer has written on your I-94 form (your “Arrival-Departure” card, which you obtain – usually from airline personnel – and complete before you speak to the immigration official). Those entering using F1 “student” or J1 “exchange visitor” visas are admitted for “D/S” (“Duration of Status”), which means “as long as you continue to follow all the rules of your category and your paperwork doesn’t expire.” But people coming in as tourists (B2) and in some other categories are given a specific expiration date on their I-94 cards, by which date they must leave the United States.
What if I have a valid tourist (B2) visa in my passport? May I use that?
Yes, but only to visit. It is illegal to pursue a study program in B2 status. If you use your B2 visa, your I-94 will say “B2” and you will not be in the appropriate legal status for on-campus employment, scholarships, or education.
What if I come in on the visa waiver program?
Same answer. Entering on a “visa waiver” is the same as entering as a tourist.
What if I want to change my status inside the United States?
Under some circumstances, this is possible. It takes time (months) and money (currently $140). It is not possible to enter on a visa waiver and then change to another status. Likewise, it is problematic to enter on a tourist visa and then change to F1 student status; this can be done only if you have explained to the immigration official that you are entering on a tourist visa in order to explore educational options and the official has written “prospective student” on your I-94.
If I change my status (to F1, for example), do I need a new visa?
No. You need a new visa only if you leave the United States and want to come back in. If you stay inside the country and maintain your new status, you do not need a visa.