September - December
Oddly enough, autumn through the holidays is the most appealing time to be in Boston, when the air is crisp and cool and the leaves are turning colors. The fall is the best time to visit Boston for beautiful foliage tours to witness the colors of the season in such a gorgeous and historic setting. Also, the arrival of tens of thousands of college students—a significant number on their own for the first time—adds a certain festive air to the streets. From late September through October, it would be worth your while to rent a car and spend a day in the hills of Western Massachusetts as a “leaf peeper.”
January - April
Unless you’re a skier, the winter can be tough time to visit Boston. It’s dark and cold, and the cultural activities tend to seriousness. There is skating at various spots around town, though, and few winter strolls are more romantic than walking through the Public Garden on a snowy evening. As for Boston's weather in the spring, most locals will tell you it consists entirely of a single muddy week between winter’s cold and summer’s heat, but they exaggerate...it’s really two weeks.
May - August
Summer is just as good a time as fall to be here, except for the heat; the college students are replaced by out-of-towners, who tend to be better behaved. From Fenway Park to the beaches, New Englanders are determined to pack in as much fun as possible before the snow flies, and you’ll find thousands by the Charles River on a summer night, listening to a Pops concert at the Hatch Shell or sailing or simply walking or biking along the riverbank. Summer is the best time to visit Boston to enjoy a movie in the park, learn to play tennis, or catch a Red Sox game.