For tourist visa, i suppose it depends on a number of factors, they basically want to be sure you'll be getting back home. I remember an old lady told me once that her visa to the US was valid for 10 years, but that seems a bit odd since the passport (on which the visa is put) is valid only for 5 years. I suppose that when you renew your passport you either get the visa-document transferred or you have to make a trip to the embassy again.And, how long do they last?