Italy has 2 high-speed train companies (Trenitalia and Italo) plus regional trains. Most tourists overpay because they don't know: booking 2-4 weeks ahead saves 50-70%, Italo is often cheaper than Trenitalia on the same route, and regional train tickets MUST be stamped in the green validation machines before boarding or you'll be fined €50. Complete train guide →
Trenitalia: State railway. Frecciarossa (high-speed, 300km/h), Frecciargento, Frecciabianca, Regionale (local). Italo: Private competitor. NTV trains, same routes (Rome-Milan, Rome-Naples, Rome-Florence, Rome-Venice), often 20-30% cheaper. Always compare both on Trainline (aggregates both companies). Advance booking: Frecciarossa Rome→Milan: €79 day-of, €29 booked 3 weeks ahead (Super Economy fare). The savings are enormous.
Regional trains (Regionale, Regionale Veloce): Paper tickets are NOT time-stamped. You MUST stamp them in the small green/yellow machines on the platform BEFORE boarding. If you don't: €50 fine from the conductor, no exceptions, no "I didn't know." High-speed trains (Frecciarossa, Italo): E-tickets with assigned seats — no validation needed. Tip: Buy on the Trenitalia/Italo apps — mobile tickets never need validation.