Nonimmigrant visas are not given automatically. An individual who wishes to travel to the United States and requires a nonimmigrant visa must appear at a U.S. consular office abroad and formally request the issuance of a visa. Visa issuance is discretionary. This means that they may reject the visa application for any reason or no reason.
Citizens of certain countries are eligible for a visa waiver if they are only coming to the United States as a visitor for 90 days or less and meet certain other requirements. Also, Canadian citizens do not require visas to enter the United States. They must, however, show proof of eligibility for the nonimmigrant category in which they claim eligibility.
For some travel, a new visa may not be necessary. If an individual is planning to go to Canada, Mexico, or certain adjacent islands only, for 30 days or less, then they may be able to travel there and return using their valid nonimmigrant status. This process is known as “automatic visa revalidation.” To be sure, there are significant limits imposed on the use of this process, but for those who qualify, it can mean the difference between an easy, casual trip or a complicated visit that includes several days dealing with a U.S. visa office abroad