As a U.S. citizen, you need a passport valid for at least six months to enter Argentina for visits of up to 90 days. Argentina operates a reciprocal entry fee scheme for citizens of countries that charge Argentineans for visas, which includes U.S. citizens. At this writing, the fee (valid for multiple entries over a 10-year period) is $160. You pay in cash or by credit card at booths near immigration, after which you receive a tourist visa stamp on your passport. You can also pay the fee online before you travel, through the Dirección Nacional de Migraciones (National Directorate for Migrations) website.
If you need to stay longer, you can apply for a 90-day extension (prórroga) to your tourist visa at the Dirección Nacional de Migraciones. The process takes a morning and costs about 300 pesos. Alternatively, you can exit the country (by taking a boat trip to Uruguay from Buenos Aires, or crossing into Brazil near Iguazú, for example); upon reentering Argentina, your passport will be stamped allowing an additional 90 days. Overstaying your tourist visa is illegal and incurs a fine of 300 pesos, which you must pay at the Dirección Nacional de Migraciones. Once you have done so, you must leave the country within 10 days. You should carry your passport or other photo ID with you at all times: you need it to make credit-card purchases, change money, and send parcels, as well as in the unlikely event that the police stop you.
Officially, children visiting Argentina with only one parent do not need a signed and notarized permission-to-travel letter from the other parent. However, as Argentinean citizens are required to have such documentation, it's worth carrying a letter just in case laws change or border officials get confused. Single Parent Travel is a useful online resource that provides advice and downloadable sample permission letters.
Dirección Nacional de Migraciones. Av. Antártida Argentina 1355, Retiro, Buenos Aires, Buenos Aires, C1104ACA. 11/4317–0234; www.migraciones.gov.ar.
Embassy of Argentina. www.embassyofargentina.us.
Single Parent Travel. www.singleparenttravel.net.
U.S. Passport Information
U.S. Department of State. 877/487–2778; www.travel.state.gov.