Visa to the United States
Going to the United States implies the issuance of a visa as one of the first legislative steps of entering any country. However, there are certain countries citizens' of which may enter the United States without issuing a visa under a Visa Waiver Program.

The Program gives the citizens of certain countries a right to enter the United States without a visa for a period of no longer than 90 days. The countries included in 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.
The program membership might be acquired by passing the online registration process via the Electronic System for Authorization (ESTA). After the document is issued, it is valid for two years and enables those citizens of indicated countries to travel to the United States under specific regulations.
Additionally, Canada, Mexico, The Turks and Caicos Islands, Cayman, Bermuda citizens may enter the United States without a visa as well.
However, there are still some regulations that shall be met by the citizens of those countries:
Bermudians and Canadians might enter the country for no longer than six months;
Those that enter the United States under a visa-free program might stay for the period of no longer than 90 days;
The citizens of the Marshall Islands, Palau, and the Federated States of Micronesia may come to the United States with the study or business purposes.
There are two types of visas valid for those entering the United States: Immigrant Visa that is applicable for the permanent is suitable for the temporary stay in the United States (tourism, business, or studying).
Notably, citizens of Libya, Iran, Syria, Somalia, Venezuela, North Korea, and Yemen were suspended from a visa issuance right after the presidential proclamation of Donald Trump made on December 4th, 2017.