The Piesting is a river in southern Lower Austria. A left tributary of the Fischa, its drainage basin is .
The sources of the Piesting are the Kalte Gang, the , and the Längapiesting, which begin south of the Schneeberg. These rivers meet in Gutenstein in the Gutenstein Alps. From there the Piesting flows east through Markt Piesting and Wöllersdorf and into the Viennese Basin.
The tributary Myrabach discharges at Pernitz into the Piesting. Between the () in the north and the () in the south, the Piesting breaks through the , a rocky ravine, and flows further eastwards through Markt Piesting and Wöllersdorf into the Vienna Basin. Near Gramatneusiedl the Piesting discharges into the Fischa.
The valley west of the (the thermal line at the Vienna Basin) in the Gutenstein Alps is known as the Piesting Valley.