Argentina Guide
Entry Requirements
Citizens of the US, Canada, the UK, Ireland, Australia and New Zealand do not currently need a visa for tourist trips to Argentina of up to ninety days, but always verify this in advance with your local consulate. All visitors need a valid passport and will have to fill in a landing card (tarjeta de entrada) on arrival, when you will be given a stamp. In theory, this could be for thirty, sixty or ninety days, but in practice it's almost always ninety. If you are travelling alone with a child you may be requested to show a notarized document certifying both parents' permission for the child to travel. Keep your landing card safe, as you'll need to show it to leave the country. If you do lose it, it's rarely a serious problem, but you'll have to fill in a new form at the border control.
On entering the country, you will also be given a customs declaration form. Duty is not charged on used personal effects, books and other articles for non-commercial purposes, up to the value of US$300. Make sure you declare any valuable electronic items such as laptop computers, as customs officers can be suspicious that you may be bringing them into the country to sell.
You can extend your stay for a further ninety days by presenting your passport to the main immigration department, Dirección de Migraciones in Buenos Aires, at Av Antártida Argentina 1350, Retiro ( 
011/4317-0237 or 4317-0238). This costs $100 and must be done on weekdays between 8am and 1pm; be prepared for a possible lengthy wait. You can do this extension, called a prórroga, once only. Alternatively, you could try leaving the country (the short hop to Colonia del Sacramento in Uruguay is a good option) and returning to get a fresh stamp.