US Customs and Border Protection (www.cbp.gov) allows a person to bring into the US up to 200 cigarettes duty-free, and each person over the age of 21 years to bring in 1L of liquor. Non-US citizens are allowed to enter the USA with $100-worth of gifts from abroad. There are restrictions on bringing fresh fruit and flowers into the country, and there is a strict quarantine on animals. If you are carrying $10,000 or more in US and foreign cash, traveler’s checks, money orders or the like, you need to declare the excess amount. There is no legal restriction on the amount that may be imported, but undeclared sums in excess of $10,000 may be subject to confiscation.
Visas are required for most foreign visitors unless eligible for the Visa Waiver Program (VWP). Note that nationals of waiver countries who have traveled in Iran, Iraq, Libya, Somalia, Sudan, Syria, or Yemen after March 1, 2011 are no longer eligible for the VWP. In addition, nationals of VWP countries who are also nationals of Iran, Iraq, Sudan, or Syria no longer qualify for a waiver.
Apart from most Canadian citizens and those entering under the Visa Waiver Program, a passport with an official visa is required for most visitors to the USA; contact the US embassy or consulate in your home country for more information about specific requirements. Most applicants have to be interviewed before a visa is granted and all applicants must pay a fee. You’ll also have to prove you’re not trying to stay in the USA permanently. The US Department of State has useful and up-to-date visa information online at http://travel.state.gov/content/visas/english/visit.html.
If you’re staying for 90 days or less you may qualify for the Visa Waiver Program (VWP); citizens of roughly three-dozen countries are eligible.