If you plan on visiting the U.S. but do not intend to stay, two designated groups are allowed visits of up to 3 months in the country. If you are from a country that is part of the Visa Waiver Program, you will likely need a valid passport and approval under the Electronic System for Travel Authorization (ESTA) a simple process you can do online.
B-1 Temporary visitors for business
This includes consulting with business associates, attending scientific, educational, professional or business conventions/conferences, settling an estate or negotiating contracts
B-2 Temporary visitors for pleasure
This includes tourism, visits with friends or relatives, medical treatment and activities of a fraternal, social or service nature
C-1 Foreign travelers in transit through the U.S.
C-2 Foreign travelers in transit to U.N. Headquarters
C-3 Foreign government officials in transit through the U.S.
D Crew members who land temporarily and depart on the same ship or plane