No visa is necessary for a stay of 30 days. Everyone requires a passport and onward ticket for entry. In the past, Americans could enter by showing a certified birth certificate, but since 9/11 Americans have also needed to present a passport.
Non-U.S. passport holders should verify visa requirements (and entry fees!) with their airline in advance as they're subject to sudden change. "Alien" women more than six months pregnant are refused entry to American Samoa. In some cases, the local immigration authorities insist on holding passports to ensure that foreigners don't overstay their visas or become a security risk.
Entry conditions are set by the Government of American Samoa—the U.S. Immigration and Naturalization Service does not exercise jurisdiction here.
Visa extensions are very difficult to obtain and work permits almost impossible unless you have a special skill someone needs, in which case your sponsor will have to post a bond. The office of the Chief Immigration Officer is in the Executive Office Building in Utulei. If you're proceeding to Hawaii from Pago Pago and need a U.S. visa, be sure to pick it up at the U.S. Embassy in Apia or elsewhere, because there's no visa-issuing office here.
Before departing Hawaii for American Samoa, cruising yachts must obtain a U.S. Customs clearance. Pago Pago is the only port of entry for cruising yachts and few try to fight their way back to Ofu and Ta'u against the wind. Tutuila is infested with the giant African snail. Customs officials in neighboring countries know this and carefully inspect baggage and shipping originating in Pago Pago.
The Giant African snail (Achatina fulica) was introduced to American Samoa and other islands during or just after WWII, perhaps deliberately as a wartime survival food or maybe by accident. Each individual has both male and female organs, and can lay up to 500 eggs at a time. This scavenger is considered an agricultural pest and possible carrier of disease. Rats and coconut crabs help control their numbers.