Lasithi (Greek: Λασίθι) is the easternmost regional unit on the island of Crete, to the east of Heraklion. Its capital is Agios Nikolaos, the other major towns being Ierapetra and Sitia. The mountains include the Dikti in the west (reaching 2,148 metres) and the Thrypti in the east (reaching 1,476 metres). The Sea of Crete lies to the north and the Libyan Sea to the south.

To the east of the village of Elounda lies the island of Spinalonga, formerly a Venetian fortress and a leper colony. On the foot of Mount Dikti lies the Lasithi Plateau, famous for its windmills. Vai is well known for its datepalm forest.

Thanks to its beaches and its mild climate year-long, Lasithi attracts many tourists. Mass tourism is served by places like Vai, Agios Nikolaos and the island of Chrysi. More off-beat tourism can be found in villages on the south coast like Myrtos, Makrys Gialos or Makrigialos, Xerokambos and Koutsouras.

Lasithi is home to a number of ancient remains. Vasiliki, Fournou Korifi, Pyrgos, Zakros and Gournia are ruins of Minoan date, Lato and Itanos were Doric towns.

The history of Lasithi can be traced over at least three millennia. The region has considerable ancient history antecedents, including the Dorian era settlement of Olous and Lato.

It has been speculated that ra-su-to, found in Linear B, corresponds to an unattested ancient Lasynthos. There is also a Lyttian tribal name Lasynthioi, presumably reflecting the same name.

Earlier proposals that it is derived from a Venetian 'la' preposed to derivatives of Lyttos (Lyttus > Tselyttus > Tselethe > Xeethe > La Xeethi > Lasithi) or Sitia (Sitia > La Sitia > Lasithi) are unlikely, as the name Lasithi was attested as early as 1211, whereas the Venetians only first arrived in Crete in 1205. Another unlikely etymology derives it from lakkos 'hole or basin' (Lakkos > Lakkidion > Latsidi > Lasidi > Lasithi).

The area was known as Laşid (Ottoman Turkish: الشيد) under Turkish rule.