The Elsa (/ˈælsə/) is a river in the Italian region of Tuscany. It flows northward to empty into the left bank of the Arno. From its source at Molli, Sovicelle, the flow of the river is low until its reaches its major tributaries at Vene di Onci and Caldane. The mouth of the river divides Frazione Marcignana of Empoli and Isola, San Miniato. The basin of the Elsa has been continuously inhabited since at least the time of the Etruscan civilization.

Elsa
Elsa River
Map of the Elsa River. Major cities of Tuscany are shown in context.
Etymology	Etruscan Hèlza,[1] comparable to Helzni-Helzunia 'noble'[2]
Location
Country	Italy
Region	Tuscany
Cities	Colle di Val d'Elsa, Poggibonsi, Certaldo, Castelfiorentino
Physical characteristics
Source	Molli, Sovicille[3]
• coordinates	43°16′49″N 11°11′06″E / 43.28028°N 11.18500°E / 43.28028; 11.18500
• elevation	580 m (1,900 ft)
Mouth	Arno
• location	Border of Frazione Marcignana, Empoli and Isola, San Miniato
• coordinates	43°43′09″N 10°52′38″E / 43.71917°N 10.87722°E / 43.71917; 10.87722
• elevation	22 m (72 ft)
Length	75 km (47 mi)[4]
Basin size	867 km2 (335 sq mi)
Basin features
Progression	Arno→ Tyrrhenian Sea

The Elsa River Basin is located between Montagnola Senese and the rolling hills of Chianti, roughly corresponding to the eponymous valley Val d'Elsa. Catchments are predominantly fan shaped.^[3] It encompasses a number of comune (municipalities) in the provinces of Florence and Siena.