In Florence and in Italy in general, you can't catch a taxi by raising your hand like in New York or London.

Taxis must be called by phone or taken at their parking lots.

The most popular companies in Florence are reachable by phone at 055/4242 or 055/4390.

You can find parking for taxis in the Piazza della Repubblica, in Lungarno Vespucci, next to the US consulate, at train station and at Porta Romana. However, in the high season this is not the best way to get one.

You can enter a hotel and kindly ask them to call a taxi for you, don't waste time hoping to catch one on the street.