The town’s origins date back to the foundation of the homonymous Abbey of San Salvatore in the Early Middle Ages. Throughout the XII century the community of Abbazia San Salvatore was formed around the abbey, under the jurisdiction of the Benedictine monks.
The town takes its name from that of the Abbey and more precisely from the Latin “abbatial” that subsequently was changed to “abbadia”, suffering the influence of the local popular dialect.The Benedictine monks of the Abbey had many land and properties and for this reason came into dispute with the Aldobrandeschi family of Santa Fiora, who wanted to take control of the abbey away from the monks.
From 1212 the inhabitants of Abbadia San Salvatore gained a certain civic autonomy. This condition lasted until 1260, year of the Battle of Monteaperti that saw the village pass under Siennese rule. Throughout the XIV century there was a certain economic development. The main activities were connected to agriculture and artisan work in wood. In this period there were also eight working mills.