Your choice of visa is determined by the purpose of your travel to the United States.
If your stay will be temporary, then you'll want to make an application for a nonimmigrant visa. This type of visa allows you to travel to a U.S. port-of-entry to request admittance from a Department of Homeland Security official.
If you are a citizen of a country that's part of the Visa Waiver Program, you may come to the U.S. without a visa if you meet certain requirements.
There are more than 20 visas available under the nonimmigrant classification, to cover the variety of reasons why someone may visit for a short time. These reasons include tourism, business, medical treatment and certain types of temporary work.
Immigrant visas are granted to those who intend to live and work permanently in the U.S. There are 4 major categories within this visa classification, including immediate relatives, special immigrants, family-sponsored and employer-sponsored.