Kostiantynivka is an industrial city in Donetsk Oblast, eastern Ukraine. It is situated on the Kryvyi Torets river. During the Soviet era, the city developed into a major centre for the production of iron, zinc, steel, and glass. Administratively, it is incorporated as a city of oblast significance. It was the administrative center of the Kostiantynivka Raion until 2020, although it did not belong to it. After the raion was abolished, Kostiantynivka was incorporated into the Kramatorsk Raion. Its population is approximately 67,350. The population declined sharply due to Russian offensives towards the city, from ~15,000 in February, to ~8500 in July 2025.