Chiusi (Etruscan: Clevsin; Umbrian: Camars; Ancient Greek: Klysion, Κλύσιον; Latin: Clusium) is a town and comune in the province of Siena, Tuscany, Italy.

[3] Chiusi came under the influence of Rome in the 3rd century BC and was involved in the Social War.

From the 11th century it was under the rule of the local bishop, and was later contended for by Orvieto and, from 1231, Siena, belonging to the latter until 1556, when it was annexed to the Grand duchy of Tuscany.

The region was devastated by malaria in the Middle Ages, and did not recover until the Valdichiana was drained in the 18th century.

It is also served by Chiusi-Chianciano Terme station on the Florence–Rome railway, which connects Chiusi to major cities in Italy.