This information is out of date! SITA (short for "Busitalia"), stopped being the bus service in Florence, Italy on October 31, 2021. Management of Florence's bus service was shifted to Autolinee Toscane, which is in charge of bus services throughout Tuscany. Busitalia has service in Umbria, Venento, and Campania, and it looks like they have one route left in Tuscany - The Mall Bus. The airport service ended in December 2022.

The SITA bus station is just a couple of hundred meters from the Santa Maria Novella train station in Florence (the main station), where you can check schedules and buy tickets. They have a website, but it is not working at the moment so I am not going to frustrate you by posting the broken link (they seemed to have changed their domain name and have some big mess going on - we will update this page when the situation changes). SITA buses run inter-city routes mostly to the south (think Chianti) and east of Florence - if you want to head to Siena and other towns on the way, then SITA is probably a good choice. They also have some tourist itineraries.

Image below courtesy of Google Maps: (this is the Autolinee Toscane bus depot!)