Piccolomini (pronounced [pikkoˈlɔːmini]) is the name of an Italian noble family, which was prominent in Siena from the beginning of the 13th century onwards.
In 1220, Engelberto d'Ugo Piccolomini received the fief of Montertari in Val d'Orcia from the emperor Frederick II as a reward for services rendered. The family acquired houses and towers in Siena as well as castles and territory in the republic, including Montone and Castiglione; the latter sold to the commune in 1321.
They obtained great wealth through trade, and established counting-houses in Genoa, Venice, Aquileia, Trieste, and in various cities of France and Germany. Supporters of the Guelph cause in the civil broils by which Siena was torn, they were driven from the city during the time of Manfred of Sicily and their houses demolished; they returned in triumph after the Angevin victories, were expelled once more during the brief reign of Conradin, and again returned to Siena with the help of Charles of Anjou. But through their riotous political activity, the Piccolomini lost their commercial influence, which passed into the hands of the Florentines, although they retained their palaces, castles and about twenty fiefs, some of which were in the territory of Amalfi and of great extent.
Another branch of the family obtained a great success in the Kingdom of Naples, becoming one of the "seven great houses" of the kingdom.