'warm water' in Azerbaijani) is a village in the Kalbajar District of Azerbaijan.

Situated in a river valley, Istisu has historically been a resort town, and during the Soviet period, it attracted people from all over the USSR to be treated at the mineral-springs baths located in the area.

[1] In the early Middle Ages, the royal baths of the rulers of Caucasian Albania were located in İstisu.

In 2018 it was reported that work has begun on a privately funded factory to produce mineral water.

[1] İstisu was returned to Azerbaijan on 25 November 2020 as part of the 2020 Nagorno-Karabakh ceasefire agreement.