The peak tourist times in Europe are April through October and the December holiday season. Be sure to book early to get your preferred itinerary and departure date.
For mild weather, visit during the spring (April and May) or fall (September and October). The temperatures still are comfortable during these months -- in Rome, for example, the highs are above 65 degrees.
If you don’t mind more of a chill, you might tour Europe during the off season, or “value season,” when airfare and accommodations are available at a much lower rate. Tours running November through March typically are priced 25% to 35% lower than peak-season departures of the same itineraries.