Like most cities in Italy, Florence is a safe destination for travellers.  There is hardly ever violent crime.  You will feel safe walking the streets of this Renaissance capital at any time of day or night.  Now, that being said, you must also use common sense.  If it's night and you're walking alone, stick to the areas and streets that have more people.  In the city's downtown, that's really not a problem, since tourists, college kids, and vendors trying to make money selling their wares are always around and about in the major piazzas and roads. Gypsies are also found in the popular tourist hangouts so take care with personal belongings. Smaller crimes happen frequently, mostly pickpocketing and drug use.  Avoid the area around the train station at night. There seems to be more questionable characters in that area as opposed to any other in the city.  Also, be aware of your surroundings when you're near Santa Maria Novella or Santa Croce at night. These are popular hangouts for Florence's disgruntled youth at night. But, if you stick around the other major sites, like the Piazza della Repubblica, the Piazza della Signoria and the Uffizi, or around Ponte Vecchio or Il Duomo, you'll be fine.  These places are lively and happy at night - people singing, playing music, laughing, eating gelato, drinking cappuccino, or just plain enjoying themselves.  You might as well do the same!