The Ionian Islands (Modern Greek: Ιόνια νησιά, Ionia nisia; Ancient Greek, Katharevousa: Ἰόνιαι Νῆσοι, Ionioi Nēsoi) are a group of islands in the Ionian Sea, west of mainland Greece. They are traditionally called the Heptanese ("Seven Islands"; Ἑπτάνησα, Heptanēsa or Ἑπτάνησος, Heptanēsos; Italian: Eptaneso), but the group includes many smaller islands as well as the seven principal ones.

As a distinct historic region, they date to the centuries-long Venetian rule, which preserved them from becoming part of the Ottoman Empire, and created a distinct cultural identity with many Italian influences. The Ionian Islands became part of the modern Greek state in 1864. Administratively today, they belong to the Ionian Islands Region except for Kythera, which belongs to the Attica Region.