Chianciano Terme does not have its own train station — the nearest railhead is Chiusi-Chianciano Terme, about 8 km away on the main Rome–Florence line. From there, local buses connect to the town; taxis are also available.
By road, Chianciano is straightforward from either direction: exit the A1 (Autostrada del Sole) at Chiusi and follow signs north to Chianciano, about 15 minutes. From Siena, it's around an hour on the SS2 and SR146. From Florence, allow about 90 minutes.
Car hire is useful here if you intend to visit the surrounding hill towns — Montepulciano, Pienza, Montalcino, and the Val d'Orcia are all within an hour's drive.