Kastoria (Greek: Περιφερειακή Ενότητα Καστοριάς, Perifereiakí Enótita Kastoriás) is one of the 74 regional units of Greece and is part of the region of Western Macedonia. Its capital is the homonymous city of Kastoria.

Kastoria is situated at the western end of Macedonia in the far north of the country. It borders the regional units of Florina to the north, Kozani to the southeast, Grevena to the south and Ioannina to the southwest. The area of the regional unit roughly corresponds to the ancient Greek region of Orestis of Upper Macedonia. The international border with the Albanian district of Korçë lies on the western edge of the regional unit.

The main mountain ranges are Gramos and Voio in the west (both part of the Pindus range) and Verno in the northeast. The Haliacmon river flows through the area. Lake Orestiada is the largest lake. The regional unit is mountainous with a pronounced continental climate, characterised by cold winters and hot summers.

The regional unit Kastoria is subdivided into 3 municipalities. These are (number as in the map in the infobox):^[1]

• Kastoria (1)
• Nestorio (2)
• Argos Orestiko (3)

• GR-15, S, Cen., NE
• GR-20/E90, S, only passes through Eptachori

• List of settlements in the Kastoria regional unit
• Dispilio Tablet