Train tickets

I have been to Italy 3 times in the last year all vacations. I found it better to buy ticket in advance and print it at home. I do this more for long distances e.g. Rome to Florence. Sometimes you will find deals e.g. 2 for 1 in first class. Short distant trip or day trips e.g. Perugia to Assissi I would buy when I get there.

http://www.italotreno.it/en

Don,

If you want to save money, you can buy your train tickets in advance (up to 120 days) at considerable savings.
Keep in mind that discounted tickets are nonrefundable and unchangeable, so your dates must be firm.

I mainly book my tickets on the Trenitalia website.

If you want to have more flexibility, and don't mind paying base price (full price), then you can wait to buy your tickets once you arrive to Italy.

Here's a very helpful website: Seat61.com

Have a great trip!

With the national railways you can almost always get huge discounts when buying your tickets for long-distance trains in advance. Those discounted tickets are tied to a specific train and are not refundable. Their website is very clear (but remember to use the Italian originals for place-names) and getting those tickets is easy and reliable (payment by credit card and emailed pdf for printing at home). If you know your travelling days, buy them as soon as possible.

Either way can work, depending on your situation.

These tickets have been on sale a while, and many discounts will be gone. So, if:
1) You know exactly which trains you want,
2) You can accept tickets that either don't allow exchanges and refunds or are limited in these actions,
and 3) Discount tickets are still available for the trains you want,

then you can book ahead online for savings. However, if you don't know which trains you are taking, or you want flexibility, or the discounts are gone on the trains you want, then there is no need to book ahead; you can buy the tickets in Italy. Once the discount tickets are gone, they don't reappear, so you will know the top price and this won't rise further.

From Rome to Florence to Venice, there are two companies (Trenitalia and Italo Treno), so check both to see who has the best remaining prices. Trenitalia: http://www.trenitalia.com/tcom-en and Italo: http://www.italotreno.it/en

On these routes, you must take the EXACT train you are ticketed for. Read about the conditions of the ticket before you buy it. If you buy a nonrefundable and non-exchangeable ticket, and can't use it for any reason, it becomes scrap paper. Some of the tickets are not refundable but are exchangeable, in the sense that you can apply their value toward a new ticket (which will probably be more expensive since the discounts sell out, but at least you don't lose the money you spent).

Note that even on the English websites, you need the Italian train station names:
Rome: Roma Termini
Florence: Firenze Santa Maria Novella (SMN)
Venice: Venezia Santa Lucia (SL)

As you can see, a bunch of us were posting at the same time.