Trains are an efficient and cheap way to get about Italy. You can look up timetables and reserve tickets online at www.trenitalia.com. The rail service, Ferrovie dello Stato (FS), operates several different types of train. You pay per mile, and each type of train has a different price.
Return tickets are the same price as two singles. It's worth comparing a few options as slower trains can be much cheaper. Sometimes for a journey that is 20 minutes longer you can halve your fare - but do be sure to have the right ticket for the train you get on.
The fastest, most comfortable service is the costly Eurostar. The most convenient way to buy tickets is from the multi-lingual machines you'll find in stations. Remember to validate your ticket before boarding.