Many people think they can show up at a U.S. embassy or border post, describe why they'd make a good addition to U.S. society, and be welcomed in. Unfortunately, this is the exact opposite of how the U.S. immigration system works.
Instead, people who want to come to the United States, whether temporarily or permanently, must determine whether they fit into eligibility categories for either permanent residence (a "green card") or for a temporary stay ("nonimmigrant visa").
Then they must submit an application--in fact, often a series of applications--to one or more of the U.S. agencies responsible for carrying out the immigration laws. These include U.S. Citizenship and Immigration Services (USCIS), which has offices across the United States (plus a few overseas), and the U.S. Department of State (DOS), which manages consulates and embassies around the world.
If you want to be able to make your permanent home in the United States, you'll need what is called permanent residence, which is evidenced by a green card. Green card holders can live and work in the United States and travel in and out, with very few restrictions (though they can't vote and can be deported if they abuse their status or break U.S. laws).
Family members of U.S. citizens make up the largest number of those who receive green cards issued each year. Others are issued to investors and workers who have been petitioned by U.S. employers or have special skills. Still other categories have a humanitarian basis, such as refugee or asylum status (which can lead to a green card), for people who are fleeing persecution. For more information, see Green Cards (Permanent Residence): Who Qualifies?.
People who want to come to the United States for a limited time need what is called a nonimmigrant visa. This lets them participate in specified activities (such as studying, visiting, or working) until their visa runs out. Students and businesspeople make up the largest groups of nonimmigrant visa holders. Nonimmigrant visas are also issued for tourists, exchange visitors, and workers with some kind of specialty that is lacking in the U.S. workforce.
For more information, see Nonimmigrant (Temporary) Visas: Who Qualifies?.
A visa is not necessary for short-term visitors from one of the Visa Waiver Program countries listed by the U.S. State Department at http://travel.state.gov. (Look under "U.S. Visa.") You can come to the United States for up to 90 days for business or pleasure purposes if you're from one of these countries. You will, however, need to present a machine-readable passport. Also, beware: The ease of your entry is balanced by the ease with which you can be kicked out--you automatically give up many rights and benefits when traveling without a visa.
To enter on a visa waiver, simply present yourself, your passport, and your ticket home to the officers you'll meet upon your U.S. arrival. If you come by land through Canada or Mexico, you'll also be asked for proof of sufficient funds to pay for your stay.
After figuring out what type of visa or green card you're eligible for, you'll need to figure out how to get it. Most people (with the occasional exception of Mexicans and Canadians or those traveling with a visa waiver) must obtain a visa at a U.S. consulate before departing for the United States. If you're already in the United States legally, you may be able to apply to adjust your status to permanent resident, or change your status to another type of visa.
Your possibilities for a visa or green card are set out under U.S. federal law. Being federal, the law is the same across the United States (though there are some variations in interpretation in different federal circuits). If you want to read the U.S. immigration laws -- which very few people actually want to do -- they're found in Title 8 of the U.S. Code, or in the Immigration and Nationality Act (I.N.A.)
In addition, information on how USCIS intends to carry out these laws is found at Title 8 of the Code of Federal Regulations (CFR). The DOS regulations are at Title 22 of the CFR. The CFR can be searched at the Government Printing Office website.
Even lawyers have trouble researching the U.S. immigration laws--they're considered to be the most convoluted and easily misunderstood portions of all U.S. law. But if you have a specific reference to a section that you'd like to read for yourself, by all means look it up, then seek professional help if you need it.
Your best bet for getting any professional help with your immigration situation is to hire an experienced immigration lawyer. Ask friends for referrals, go to the website of the American Immigration Lawyers Association (AILA), or go straight to Nolo's Lawyer Directory for a list of immigration attorneys in your geographical area.
Whatever you do, don't go straight to USCIS for advice. The people who staff their front desk are not all well trained and, if they give you wrong information, they take no responsibility, even if it causes your deportation or destroys your chances of immigrating. This happens!
Many of these immigration laws are described in U.S. Immigration Made Easy, by Ilona Bray (Nolo). This book discusses how to obtain many different visas, including the K-1 visa for fiancés, the B-1 and B-2 business and tourist visas, the H-1B, H-2B, and H-3 visas for temporary specialty or agricultural workers, the L-1 visa for intracompany transferees, the E-1 and E-2 visas for treaty traders and investors, the F-1 and M-1 visas for students, the J-1 visa for exchange visitors and scholars, and the O, P, or R visas for temporary workers, as well as how to get a green card through a family member, through the Diversity Visa Lottery, or as an asylee or refugee.
One of the worst things you can do to your chances of getting a visa or green card is to lie, either on paper or during an interview with a U.S. consular or border or other immigration officer or inspector. Lies can have both immediate consequences, such as not being able to enter the U.S., and long-term consequences, such as not being able to get a green card -- ever. Or, even if you were to obtain a green card through a lie, you might later be denied U.S. citizenship when your file is reviewed in connection with your application for naturalization and the lie is discovered--which could also lead to your removal from the United States.
No matter what eligibility category you fall into -- whether you've married a U.S. citizen, received a job offer, or been accepted to a school -- the United States has the right to say no. And not just because there's something wrong with your application. The immigration law contains a list of things, like crimes and certain diseases, that makes someone inadmissible. For more information, see Inadmissibility: When the U.S. Can Keep You Out.
For a complete guide to how the immigration system really works, read U.S. Immigration Made Easy, by Ilona Bray (Nolo).