What is a visa and what rights does it provide?
This is one of the most fundamental questions in immigration law. A visa is essentially a provisional permit to enter the United States.
Does a visa guarantee that I can enter the United States?
No unfortunately it does not guarantee entry. It's important to note that the visa does not guarantee one the right to enter the United States. United States Customs and Border Protection (CPB) can deny someone the right to enter the country based on a number of factors, when they inspect the person at the port of entry.
Who needs a visa?
Almost all foreign nationals wishing to enter the United States need a visa. The visa is both literally and figuratively attached to one's passport—it’s placed inside the passport, and for the visa to remain valid, one's must have a valid passport. If your visa is in an expired passport it is still valid, but you must present it with your valid passport. Frequently your expired passport containing your valid visa is attached to your valid passport.
What is the difference between a visa and a Green Card?
While there are many different specific visas, each visa belongs to one of two categories: immigrant and nonimmigrant. Nonimmigrant visas are temporary — they allow a foreign national to come to the United States for a specific reason, for a limited amount of time. Immigrant visas, on the other hand, offer a "Green Card.” A Green Card gives one the right to live in the United States permanently as a "permanent resident."
What is an I-94, how is it different from a visa, and what impact does it have on my length of stay in the United States?
The I-94 is called the Arrival/Departure document, and it's issued to individuals entering the United States with a nonimmigrant visa. The I-94 is obtained when a person arrives in the US, issued by the Customs and Border Protection (CBP). It's the I-94 card, not the visa, which actually gives one the right to enter and remain in the United States. It's also the I-94 card that determines how long one can remain in the country. In other words, the validity period of the visa may be different—either shorter or longer—than the date provided on the I-94 card.