| Official Name: | Istisu |
| Pushpin Map: | Azerbaijan#East Zangezur |
| Pushpin Mapsize: | 300px |
| Subdivision Type: | Country |
| Subdivision Name: |  Azerbaijan |
| Subdivision Type1: | District |
| Subdivision Name1: | Kalbajar |
| Timezone: | AZT |
| Utc Offset: | +4 |
| Coordinates: | 39.9481°N 45.9617°W |
İstisu (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.[2] There is a resort in the town, known as Istisu resort.
The village was located in the Armenian-occupied territories surrounding Nagorno-Karabakh, coming under the control of ethnic Armenian forces during the First Nagorno-Karabakh War in the early 1990s. The village subsequently became part of the breakaway Republic of Artsakh as part of its Shahumyan Province, referred to as Jermajur (Armenian: Ջերմաջուր). In 2018 it was reported that work has begun on a privately funded factory to produce mineral water. İstisu was returned to Azerbaijan on 25 November 2020 as part of the 2020 Nagorno-Karabakh ceasefire agreement.