3 weeks in Italy - in which order would you travel?

I would probably start in the south and move north, to chase the cooler weather. Definitely train.

I agree with Michael if you care about temperature... we were in Rome in late July and it was HOT. Side note: That is a VERY long vacation for just a FEW destinations (plus side trips). I was able to enjoy those three cities in about nine days--including train travel--two is sufficient for Venice, one or two for Florence, and four for Rome. I don't know what your objective is... perhaps utter relaxation or in depth study of each place... but I fear your teenager will get bored with such a slow pace.... just my two cents!!! Pete

@Michael - great suggestion on the heat @ Pete - i hear you on the teenager boredom factor. will look into some other sites and locations. thanks for the tip mike

I think it's refreshing to see an Italian itinerary on here that's not rushed. That said, I think you could easily add one to two more destinations and still not be too rushed. On my first trip to Italy I did these three cities and I did 4 nights Venice (one more might have been perfect), then 5 in Florence and Rome. I thought that was a good solid introduction and I took minimal daytrips. I only know myself and I would not have gotten bored with a week in those three incredible cities. But you do have room to add a couple more stops, too, should you want to. Everything there depends on who you are and what your family enjoys. I've been to a lot of cities in Italy at this point and can't say I've found any of them to be boring, it just depends on what you might like.

Spend at least 4 days in Florence! There are thousands of American students there so watch the daughter! LOL. You can day-trip to Sienna, which will take up a day.Take the wife/daughter to Ponte Vecchio and let them look at the millions and miollions of diamonds and sparkling gold/diamonds. Unbelievable! Have a drink @ the Lemon Bar overlooking the Arno (lots of young ones there) go to la piazza della signorina at night.....see the Uffizzi...the "Real David" Sign up for a wine tour, that'll take up a day. Florence is a lovely place......... Rome, another four days make sure you see the usual sites, that will take 3 days Vatican, Vatican Museum, Sistene Chapel.........walk through the Campo di Fiori beautiful flowers for sale, as well as many tourist items, plus fantastic jars of "spreads" that are totally Italiano to bring home and put on crackers at your next party then on to Piazza Navona in my opinion, the most beautiful fountain/piazza in all of Italy!
From there or another night, Trastavere very young, very vibrant the teenage daughter can't help but like it, and I haven't even mentioned Colosseum! 2 days in Venice will do it!

If you're there during the warm months, take the family to Riccioni/Rimini -- beach towns on the Adriatic. Family-friendly, but also some discos. We were there and had a very great time! These are to the North and as I've said the Adriatic side!
Near Venice if you want to look on the map and figure out logistics.

mike, For a first trip to Italy, I'd normally suggest starting in Venice and moving south, as the culture becomes more "intense" as you move south. However, given the time of year you'll be travelling, starting in Rome would be a good idea. I suspect it's going to be "warm" in either case! As the others have mentioned, with three weeks you'll have time to include a few more destinations. As you move north, you could consider adding Orvieto, Siena, the Cinque Terre, Lago di Como or Lago Maggiore (which could include a day trip to Switzerland), Verona or the Dolomites. Which of these to choose will depend for the most part on what your group is interested in seeing, and of course subject to the "boredom factor" of your daughter. I'd suggest having a look at the Italy 2012 Guidebook as that has a lot of great sightseeing information, including ways to minimize queues at locations such as the Colosseum. Good luck with your planning and happy travels!

I'm wondering if it might be better, weatherwise, to start in Venice. I don't think it matters much in Rome or Florence - it will be hot. But Venice might just be better earlier in the summer - I'm reminded of reports I've heard about mosquitoes and stagnant water . . . Besides which, I think Venice is a better place to start the trip - more relaxed for your first day or two while re-energizing after the flight and getting used to the time difference. It would be nice to add 2-3 nights in another town, to get a better feel for the "evening experience" when the locals have their dinner and passagietta (I know I'm spelling that wrong) - Verona (though it will be opera season) and/or Siena.

will you be flying open jaw? I agree with other posters that with 3 weeks you could add another location or two without being rushed you could consider flying into Rome and out of Venice or out of Milan
you could add Cinque Terre, Lake Como, Verona...just to name a few

Ciao Mike! Congratulations on choosing a trip that will allow you lots of time to see the sights and soak in the Italian culture. A week each in Rome, Florence and Venice is wonderful, allowing plenty of time for both day trips and sightseeing. I agree that you should start in Rome and end in Venice, considering the time of year you are traveling. Since you will be in each city an extended period of time, consider renting an apartment in each city. More room and the ability to do laundry are highlights!

We always end in Venice. It's very calm and relaxing for us after the traffic and vespas in other cities.

I usually tell people to start in Rome. Its more stressful and chaotic and your sightseeing list more full. I think its an easier city to do when you are still fresh and excited to be there. It can be a busy way to end a trip. I prefer to end with a more relaxing stop with fewer sights to see and more time wandering. But for those that are really nervous about the trip and how to get around, it can be easier to figure it out in a slower city where you have fewer sights to fit in. Then by Rome you have it figured out.