Kastos (Greek: Καστός) is a Greek island and a former community east of the island of Lefkada, Ionian Islands, Greece. Since the 2011 local government reform it is part of the municipality Lefkada, of which it is a municipal unit.Until 1974, when it became part of the Lefkada Prefecture, the island was administered under the Cephalonia Prefecture (Ithaca province). The nearest island is Kalamos, with a deep channel between them; the mainland is approximately 5 kilometres (3 miles) to the northeast in Aetolia-Acarnania.
The island has only one village, the homonymous Kastos, located on its east coast. It has a population of about 80, involved mainly in fishing and tourism services. During the summer Kastioti of the diaspora return for holidays and, together with the fluctuating visitors arriving on yachts, form its seasonal character. The island is 7 km (4 mi) long from north to south, and 800 m wide. The area is 5.901 square kilometres (2.278 sq mi) and its highest point is 142 metres (466 feet) over the Mediterranean Sea level. Kastos has two churches, Agios Ioannis Prodromos, which is located in the centre of the village, and Agios Emilianos, located about 4 km (2 mi) northeastern of the village. Agios Ioannis church is decorated with wall paintings from the notable Eptanesian painter Spyridon Gazis. Also, the island has two windmills and three olive presses, none of them functioning anymore
The island has a range of facilities such as three bars, four restaurants and a small gift shop. All facilities are open during the summer, however most close during the winter months of the island. The island has two harbours for boat mooring, one located on the front of the island, the other located at the back.