Tickets are valid for 24 hours - though the buses only run from 0900 until about 2100. We found that by catching our first bus after an early lunch one day, riding it until about 1800 in the evening and then picking up the first bus in the morning and using our ticket right up to the last minute of the 24 hours, we really felt we got better use out of it. The overnight break suited us very well.
There are several of these hop on/hop off buses operating in Rome. The one run by City Sightseeing (the biggest players in this game with operations in cities all over the world) has 2 routes that interconnect at set points with the one ticket valid for both routes. Disposable headphones are included and commentaries offered in several languages. We found this worked well - the commentary was fairly basic but quite broadranging and there were no problems with clarity.
The open top double-decker buses offer great view, though taking photos can be a bit hit and miss. You wouldn't want to sit downstairs however- we did this for a short time when a sudden rain shower hit and the view is very restricted. I could see this being a problem later into the season as the crowds build up.
You can start your tour at any one of the stops along the way. You'll be given your headphones - keep them with you as you hop off - and a card that gives you the times the buses will be at each of the stops along the different routes.
Check the website here for current prices, times, etc.


