The Hassegau was a medieval shire (Gau) in the Eastphalia region of the Duchy of Saxony. It was located in the duchy's southeastern corner; confined by the Saale river to the east and its Unstrut and Wipper tributaries to the south and north. Its most important town was Merseburg. In present-day borders, it is in the southeastern part of Saxony-Anhalt.