In order to enter the United States you are required to have a visa, issued by a United States Embassy or Consulate in your home country. Visitors to the United States who do not intend to become citizens or permanent residents, need to receive a "nonimmigrant visa." The United States government issues many different types of nonimmigrant visas, and the type of visa issued indicates the privileges and responsibilities you have as visitor to this country. For example, if you are planning to come to the United States as a student, attending courses at a college or university (or one of several other types of institutions) you will apply for and receive an F-1 (student) visa. If you are planning on coming for short-term specialized training (for example in computer maintenance or learning how to fly an airplane) you will likely receive an M-1 "training" visa. If you are planning on coming as a short term student in an exchange between your University and one in the United States, or you are a visiting professor, or you plan on coming to do research then you will receive a J-1 "exchange visitor" visa.
Each Visa Type carries with it very specific privileges, requirements, and obligations. The United States government expects you to assume full responsibility for knowing the regulations which go along with your specific visa, and maintaining your good standing in this country by living within those regulations. You can get a good idea of these requirements by reading the information. You should also know any special requirements of your sponsoring institution or organization.
Your visa is an important document which may allow you to enter and leave the United States as well as to perform all of the activities and functions which bring you to the country in the first place. Please make sure that you know all of the regulations concerning your visa and any important dates relating to it (for example whether or not it expires and what you need to do if that expiry date is approaching.)
We look forward to welcoming you as a visitor in the United States.