Sax (Spanish pronunciation: [ˈsaks], locally: [ˈsas]. Valencian: Saix [ˈsajʃ]) is a municipality in the comarca of Alt Vinalopó, province of Alicante, Valencian Community.

The origin of the name Sax is uncertain, although it has been related to the Latin term saxum (rock), due to the pointed rocky mass on which its castle stands, and around which the town appeared. The term has also been related to the Segisa that Ptolemy located in Bastetania. It is possible that during the Roman period there was an establishment or inn in Sax next to the Via Augusta. The current pronunciation is /saks/ although traditionally it was /sax/, as confirmed by the gentilic name Sajeño.

There are archaeological findings in the area dating to the Bronze Age, as well as an Iberian necropolis and remains of Roman villas.

In the later stages of the Reconquista, Sax was at the focus of tensions between Castile and Aragon, since James I of Aragon conquered it from the Moors though it should have been reserved to Castile under the treaties of Tudilén and Cazorla.