http://travel.state.gov/visa/temp/types/types_1262.html
Generally, a citizen of a foreign country who wishes to enter the United States must first obtain a visa, either a nonimmigrant visa for temporary stay, or an immigrant visa for permanent residence. The visa allows a foreign citizen, to travel to the United States port-of entry and request permission of the U.S. immigration inspector to enter the U.S. The "visitor" visa is a nonimmigrant visa for persons desiring to enter the United States temporarily for business (B-1) and for pleasure or medical treatment (B-2).
As examples, if the purpose of your planned travel is recreational in nature, including tourism, amusement, visits with friends or relatives, rest, medical treatment, and activities of a fraternal, social, or service nature, then a vistor visa (B-2) would be the appropriate type of visa for your travel. As additional examples, if the purpose for your planned travel is to consult with business associates, travel for a scientific, educational, professional or business convention, or conference on specific dates, settle an estate, or negotiate a contract, then a business (B-1) visitor visa would be the appropriate type of visa for your travel. After reviewing this website information, should you need additional information about business related (B-1) visitor visas, select Business Visa Center .
Changes introduced shortly after September 11, 2001 involve extensive and ongoing review of visa issuing practices as they relate to our national security. Visa applications are now subject to a greater degree of scrutiny than in the past. So it is important to apply for your visa well in advance of your travel departure date. Select Getting Your Visitors Visa – Information You Need to Know to learn more.
Foreign travelers who are citizens from certain eligible countries, may also be able to visit the U.S. without a visa on the Visa Waiver Program. Review the information below about Visa Waiver.
Persons planning to travel to the U.S. for a different purpose such as students, temporary workers, crewmen, journalists, etc., must apply for a different visa in the appropriate category.
NOTE: Representatives of the foreign press, radio, film, journalists or other information media, engaging in that vocation while in the U.S., require a nonimmigrant Media (I) visa and cannot travel to the U.S. using a visitor visa and cannot travel on the visa waiver program, seeking admission by the DHS immigration inspector, at the U.S. at the port of entry.
The Department of State recommended first source of visa information is this Visa Services internet site. Please review this information carefully. For an additional visa overview, select the Department of State visa portal site, Destination USA . As explained below, it is also recommended that you review the Embassy Consular internet site, for the country where you will be applying for your visa.
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read the highlighted portion the source link is provided. visitor visa includes visiting family and friends, activities realetd to fraternal social events etc... that would mean birth of a granchild, so these are reasons enough according to the state dept as well as USCIS.