Visa Regulations in the United States
When entering the United States, so as any other country, the one shall consider to check whether s/he needs a visa first. Therefore, visa possession will be the first thing that will undergo testing on the entrance to the country. However, as mentioned previously, the citizens of certain countries have a right to enter the United States without issuing a visa.

A Visa Waiver Program, valid on the territory of the United States since 1988 when the Congress passed legislation for its issuance, allows the citizens of some countries to enter the United States visa-free in case if s/he travels to the USA with the business or tourism purposes for no longer than 90 days. The countries that are a part of the program are: Australia, Andorra, Austria, Brunei, Belgium, Chile, Czech Republic, Denmark, Estonia, France, Finland, Germany, Greece, Hungary, Ireland, Iceland, Italy, Japan, Latvia, Luxembourg, Liechtenstein, Lithuania, Monaco, Malta, Netherlands, New Zealand, Norway, Portugal, San Marino, Slovakia, Slovenia, South Korea, Spain, Sweden, Singapore, Switzerland, Taiwan, United Kingdom.
To acquire the program membership, the one may go through the online process via the Electronic System for Authorization (ESTA). After the document is issued, it is valid for two years after the date of issuance and allows to travel to the United States.
The citizens of other certain countries as Canada, Cayman, Bermuda, Mexico, The Turks and Caicos Islands may enter the United States without a visa under the country's political policy.
However, there are still regulations that shall be met by the citizens of those countries when coming to the United States:
Bermudians and Canadian may stay in the United States for no longer than six months;
The limit a maximum of 90 days is applicable for those that enter the United States under a visa-free regime;
Moreover, citizens of Palau, the Marshall Islands, and the Federated States of Micronesia can come to the United States with the study or business purposes in case if they provide a passport that is valid for six months after the entrance to the country.
There are two types of visas available for those entering the United States: Immigrant Visa which is obtained for the permanent stay in the United States, and Non-Immigrant Visa which is acquired with the purpose of the temporary visit in the United States (tourism, business, or studying).
Notably, citizens of Libya, Iran, Syria, Somalia, Venezuela, North Korea, and Yemen are deprived of the receipt of a visa after the presidential proclamation of Donald Trump that was officially activated on December 4th, 2017.