Lefkada (Greek: Λευκάδα, Lefkáda, [lefˈkaða]), also known as Lefkas or Leukas (Ancient Greek and Katharevousa: Λευκάς, Leukás, modern pronunciation Lefkás) and Leucadia, is a Greek island in the Ionian Sea on the west coast of Greece, connected to the mainland by a long causeway and floating bridge. The principal town of the island and seat of the municipality is Lefkada. It is situated in the northern part of the island, approximately 25 minutes by automobile away from Aktion National Airport. The island is part of the regional unit of Lefkada.

Lefkada measures 35 kilometres (22 miles) from north to south, and 15 kilometres (9 miles) from east to west. The area of the island is about 302 square kilometres (117 sq mi), the area of the municipality (including the islands Kalamos, Kastos and several smaller islets) is 333.58 km² (128.80 sq mi). Its highest point is the mountain Stavrota, at 1,158 metres (3,799 feet) above sea level, situated in the middle of the island. The east coast section of the island has the small resorts of Lygia, Nikiana and Perigiali, all north of Nidri, the largest resort on the island. It is set in a sheltered location, with views across to Skorpios (formerly owned by Aristotle Onassis), Meganisi and other small islands, as well as the Greek mainland. The main coastal road from Lefkada to Vasiliki runs through the village, although a bypass has now been completed which skirts the village to the west. There are regular car ferries to Kefalonia, Ithaca and Meganissi.

20 kilometres (12 miles) south of Nidri is the resort of Vasiliki, a windsurfing center. There are ferries to Kefalonia and Ithaca from Vasiliki. South of Vasiliki is Cape Lefkada, where Cephalus and the Greek female poet Sappho allegedly leapt to their death from the 30 m high cliffs on two separate occasions.

The famous beach of Porto Katsiki is located on Lefkada's west coast. Lefkada was attached to mainland Greece (see below about Homer's Ithaca being Lefkada). The Corinthians dug a trench in the 7th century BC on its isthmus.

The southernmost tip of the island is called Cape Dukato, a name sometimes applied to the whole island.

The island has a typical Mediterranean climate with hot summers and cool winters, or Csa according to the Köppen climate classification system.

The island is linked to Odysseus, the hero of Homer's Odyssey, who ruled it and neighbouring islands from Ithaca. The German archaeologist Wilhelm Dörpfeld, having performed excavations at various locations on Lefkada, was able to obtain funding to do work on the island by suggesting that Lefkada was Homer's Ithaca, and the palace of Odysseus was located west of Nydri on the south coast of Lefkada. There have been suggestions by local tourism officials that several passages in the Odyssey point to Lefkada as a possible model for Homeric Ithaca. The most notable of these passages, pushed by the local tourism board, describes Ithaca as an island reachable on foot, which was the case for Lefkada, since it is not really an island, being connected to the mainland by a narrow causeway. According to Strabo, the coast of Acarnania was called Leucas in earlier times.

The ancient sources call Leucas a Corinthian colony, perhaps with a Corcyraen participation. There was a cult to Apollo Leucatos at the south western cape of the island, where white cliffs stand, that may have given its name to the island. This was a site where criminals were thrown (hence "Leucadian trial") in order to judge their guilt or innocence from their injury at the fall. Furthermore, according to legend, it was the jumping spot of Sappho when she committed suicide out of frustrated love and also that of Artemisia of Caria, and therefore may have some connection to Aphrodite.