The nearest international airport is Florence (90 km north), with Pisa (105 km) and Rome Fiumicino (230 km) as alternatives. Direct buses (Tiemme) run from Florence airport to Siena in about 90 minutes; they are easier than the train, which requires a change at Empoli.
Coming by car, take the SS222 (Chianti road) from Florence for the scenic route, the superstrada Firenze-Siena for speed. Parking in the centre is strictly controlled — leave the car at one of the perimeter car parks (San Francesco, Il Campo, Santa Caterina, Il Duomo) and walk or take the moving stairways into the centre.