In 2008, Italy rebranded its high speed trains as the Frecciarossa (red arrow) and in the following years the network has been expanded to connect Turin with Naples, via Milan, Bologna, Florence and Rome.
After some teething problems, the Flecciarossa trains now provide an exceptionally good service, both comfortable and fast. They are also quite expensive. However, one can alleviate the issue of ticket prices by planning well in advance and taking advantage of the special offers that are available when booking via the Trenitalia website. In general, these reduced price tickets cannot be changed, but the savings can be dramatic especially if you are flexible regarding date and/or time of travel.
From 2012, a new competitor has appeared on the Italian railway scene. These are the Italotreno high speed trains which run between main centres. It’s definitely worthwhile to compare prices between Trenitalia and Italotreno for a give day and time since the standard prices of Italotreno can be lower. HOWEVER note that Italotreno often runs between suburban stations rather than the main stations, making connections between trains problematic.
More about Italo trains.