As is the case with much of Italy, the nightlife starts around 6 or 7pm with a phenomenon called aperitivo, which is similar to the American happy hour where food of some sort (and it really is quite a range of both quantity and quality, depending on the place) is included in a marked up drink price. There are three areas we recommend, all of which provide a good variety of aperitivo choices and continue providing music, beverages, and social interaction until the night grows old. The first is Santo Spirito in the Oltrarno neighborhood. Across the Arno River from the historic city center, Santo Spirito is a large piazza known for its collection of restaurants, cafes, and bars. Sit back during the summer and drink an outdoor Spritz or test your palate with house Chianti in a number of locations. The Santa Maria Novella neighborhood has more of the same choices and is off-the-beaten-track enough where you'll actually see a few locals if you're hanging out in the area. Located near the train station, there are a handful of great places to grab a beer or glass of wine as you move toward the Arno; you'll also encounter the most reliable club (Space) and the most enticing rock vibes (Il Trip Per Tre) in town if you're in the neighborhood. Lastly, the Santa Croce neighborhood south of the historic center is worth a gander. Just walk south of the main piazza and you'll encounter plenty of choice, although these are the type of places that get really sloppy come 2am. Jet a few blocks across the river for a few more classy locations in the San Niccolò neighborhood on the river if you aren't up for dodging the stumbling masses.
Browse our neighborhood pages for more specific establishments, as well as further inspiration in your attempts to find the right kind of nightlife in Florence for you.