Best time to visit

Well... as always there is no way to predict the weather, but one of my favorite times to visit is either late April or early to mid-May. There are still tourists, but certainly it is more pleasant than the heat of summer. As for itinerary, it is best to come back with some sort of idea of the cities you would like to see and 2 weeks or 3 weeks is a huge difference. 14 day trip vs 21 days....

May is great because there are flowers blooming everywhere and it's usually warm enough without being too hot. As far as how many cities, plan to spend at least 2 nights per city/village, with 3 nights giving you a much better experience. Rome deserves 4 nights, IMHO.

We went once in late April and another time in early May and loved it. Temps were basically between 63-73 during the day for the most part. So nice weather for touring but not the summer crowds.

I would begin the trip mid-April. In 2009, second week in May, African Heat Wave, mid-90's, pure hell!

Gioid for you not wanting to "rush." This is no place to rush! 14 days: no more than 4 locations, minimum 2 nights, preferrably 3 nights, in smaller towns, 4 or 5 in larger (Rome, Venice, Florence, Sorrento area). 21 days: 6 locations maximum. You might do this with 3 weeks: - Venice (4 nights) - Cinque Terre (3) - Tuscan or Umbrian hilltown like Cortona, Montalcino, Assisi (3) - Florence with daytrip to Siena, maybe a wine tour day (4) - Rome (5)
That's 19 nights. If you really have 21 nights, add a small town for 2 nights (Orvieto comes to mind), or add nights on to someplace you are already staying. (I can't stay long enough in Venice and clearly think Rome is worth a lifetime!) It may seem 5 locations isn't "enough" in 3 weeks, that you'll want to see "more" of the country. But you will see more if you change locations less often. You will experience far more by staying 3 or more nights in one place.

I loved mid October to early November. Comfortable days, cool evenings.

Thanks to everyone who has posted. This will definitely give me a good starting point for planning my trip.

Having done both the spring and fall in Italy several times, I'd vote for the fall... mostly because hotels are quieter. During May trips, I've several times shared budget hotels with large, noisy groups of touring school kids, since that seems to be when the Europe schools do their extended field trips. I think I'm a reasonably tolerant person, but the experience a couple of times in Florence and one time in Venice was enough to convince me to stick to the fall whenever possible. How much you fit in depends on your travel style. I'd much rather see fewer things so I can experinece where I am, but I know my approach would bore some others to tears. On my initial visits to the major cities, I spent 10 days each in Rome, Venice, and Florence, and I would have welcomed more time. But with 3 weeks, you could certainly cover more than that, if you prefer a less-in-depth visit. also, each time you change cities, assume you'll lose from 1/2 day to a full day, depending on transit options.

May and late September-end of November are great. Where you go depends on what you want to see. Getting to hotels and checking in eats up time, so we stay in a few cities and make day-trips to smaller towns or even rural areas. For example, stay in Bologna and make excursions to Modena, Ferrara or even Ravenna. Italy has great train and bus services with cheap point-to-point tickets and convenient schedules. The regional trains are a great travel bargain. And with day-trips you are not encumbered by luggage getting on and off trains or buses. Look for lodgings with easy access to a train or bus station. use the Trenitalia website to check schedules and prices for regional trains. Be flexible, as there may be a one-day or 6-hour strike. For lodging, check out apartments. We get more space and lower price per night than a hotel (2-bedroom flat in Rome center for 70 Euros night in October). Visit the local markets--they are one of the most entertaining attractions in any city in Europe (even the "supermarkets" are fun!). Be a people-watcher--Italians are fantastic and very glad to give directions and suggestions.

I was in Italy in May and toward the end of the month it turned quite cool. I've found late September-October to be more reliable. As for feeling rushed, that's a variable only you can predict. If you like a home base, choose 3 cities and daytrip (perhaps 4 cities if you have 3 weeks).

Two times there mid-late Sept - weather (for us) was amazing - only thing is I would like more daylight hours...but we have had such great weather that time of year

Longer days is another reason to go in May. But September does have its advantages. That's when we were in the Cinque Terre and they were bringing in the grape harvest.