Trains are genuinely the easiest way to cover ground in Italy with a pet — no security lines, no cargo hold, and considerably more space than a car for a long journey. Small pets in a carrier no larger than 70 x 30 x 50cm travel free on almost every Trenitalia service and class, limited to one carrier per passenger, and the animal has to stay inside it for the whole journey.
Larger dogs travel on a leash and muzzle rather than in a carrier, but need a paid ticket. Pricing works out to roughly €5 for weekday travel or as little as €1 on Saturdays — generally about half the standard second-class fare, though it varies by train type. Larger dogs aren't permitted in Executive or Premium service levels on Frecciarossa trains, in dining cars, or on some regional trains during the Monday–Friday 7–9am commuter rush.
Buying the ticket is simple: select the 'travelling with your dog' service option on the Trenitalia website, app, at a station ticket office, or at a self-service machine, at the same time as buying your own ticket.
Italo, the privately-run high-speed operator connecting cities like Milan, Turin, Venice, Florence, Rome, and Naples, follows a similar structure: small pets in a carrier ride free, larger dogs need a paid ticket for a dedicated space, bookable via the Italo website, app, a ticket office, or by phone through Pronto Italo (060708). Travelling off-peak tends to be calmer for a larger dog on either network, simply because carriages are less crowded.