Before entering the United States, an individual shall obtain the U.S. visa first that will be placed in the passport of an individual. However, some travelers may enter the country without a visa due to special visa-free regulations.
Notably, a visa does not give the guarantee that the one may enter the United States in case if it does not indicate the consular officer at a U.S. Embassy confirmation that the one is eligible to enter the country for specific purposes.
There are two types of visas Non-Immigrant and Immigrant Visa which are each divided into subcategories.
Immigrant Visa is given for the permanent stay in the United States.
Non-Immigrant Visa is given for the temporary stay in the United States.
Under a Visa Waiver Program the citizens of the following countries do not need a visa to enter USA: Andorra, Australia, Austria, Belgium, Brunei, Chile, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Japan, Latvia, Liechtenstein, Lithuania, Luxembourg, Malta, Monaco, Netherlands, New Zealand, Norway, Portugal, San Marino, Singapore, Slovakia, Slovenia, South Korea, Spain, Sweden, Switzerland, Taiwan, United Kingdom.
Those visitors may enter the country without a visa in case if s/he stays for maximum 90 days for business and tourism purposes; the passport of the person shall meet all applicable requirements.
Citizens of Canada, Mexico, Bermuda, Cayman, The Turks and Caicos Islands do not require a visa when entering the USA as well.
However, there are some details applicable to various countries; those are listed below:
Canadians and Bermudians can stay on the territory of the United States for a maximum of six months;
For visitors that have entered the United States can remain for a maximum of 90 days;
Citizens of the Marshall Islands, Palau, and the Federated States of Micronesia may enter the country for business and study purposes in case if they may provide a valid passport.
On September 24th, 2017 a president Donald Trump has signed a proclamation that suspended the issuance of visas to nations of individual countries: Iran, Libya, North Korea, Somalia, Syria, Venezuela, and Yemen. After several disputes of several judges, the proclamation went into effect on December 4th, 2017.
Due to lack of corporations, the visa issuance was restricted on September 13th, 2017 to the nations of the following countries: Cambodia, Eritrea, Guinea, and Sierra Leone.
An Order signed on January 27th, 2017 and expired on 27th of April 2017 has announced an entry ban for nations of several countries: Iran, North Korea, Syria, Sudan, Iraq, Libya, Somalia, Yemen are the countries of particular concern.