Technically, the law allows you to apply for a B visa at any U.S. consulate you choose. From a practical standpoint your case will be given greatest consideration at the consulate in your home country. Applying in some other country creates suspicion in the minds of the consular officers about your motives for choosing their consulate. Often, when an applicant is having trouble at a home consulate, he will seek a more lenient office in some other country. This practice of consulate shopping is frowned on by officials in the system. Unless you have a very good reason for filing elsewhere (such as a temporary job assignment in some other nation), it is smarter to file your visa application in your home country.
Furthermore, if you have ever been present in the U.S. unlawfully, in general you cannot apply as a third-country national. Even if you overstayed your status in the U.S. by just one day, you must return to your home country and apply for the visa from that consulate. There is an exception. If you were admitted to the U.S. for the duration of your status (indicated by a “D/S” on your I-94 form) and you remained in the U.S. beyond that time or purpose for which your status was conferred, you may still be able to apply as a third-country national.
You will be barred from third-country national processing only if an immigration judge or INS official has determined that you were unlawfully present. Because of the ambiguity, you may find that your success in applying as a third-country national will depend on your country, the consulate and the relative seriousness of your offense.
In many consulates, you can simply walk in with your passport and supporting documents, fill out the application form while you are there, and get your B visa within a few days. Other consulates insist on advance appointments. Most consulates in Canada and Mexico require you to come up to a week in advance to receive an appointment. A few, like London, will process visa applications by mail. Since procedures among the consulates vary, you should always telephone or check their website in advance to find out about local policies. (U.S. consulates in Canada require you to make an appointment by phone.) Allow plenty of time for a decision—security checks can add weeks or months to the processing time.
While there is a definite difference between B-1 and B-2 visas, the two are frequently issued together. In fact, the machine used to print the visas in your passport groups both B-1 and B-2 on the same stamp. If the consulate wishes you to have only one, the other will be crossed out by hand in your passport.
On entering the U.S. with your new B visa, you will be given an I-94 card. It will be stamped with the dates showing your authorized stay. In the past, you were normally permitted to remain in the U.S. for six months. Under the USCIS’s proposed new regulations, however, you will be allowed six months only if you can show a specific reason that you need that much time. Thirty days may become the more commonly granted period of stay—and there are reports that some airport INS officers are already reducing travelers’ permitted stays to 30 days. Each time you exit and reenter the U.S., you will get a new I-94 card with a new period of authorized stay.