Messenia or Messinia (məˈsiːniə ; Μεσσηνία mesiˈni.a) is a regional unit (perifereiaki enotita) in the southwestern part of the Peloponnese region, in Greece. Until the implementation of the Kallikratis plan on 1 January 2011, Messenia was a prefecture (nomos) covering the same territory. The capital and largest city of Messenia is Kalamata.
Messenia borders on Elis to the north, Arcadia to the northeast, and Laconia to the southeast. The Ionian Sea lies to the west, and the Gulf of Messinia to the south. The most important mountain ranges are the Taygetus in the east, the Kyparissia mountains in the northwest and the Lykodimo in the southwest. The main rivers are the Neda in the north and the Pamisos in central Messenia.
Off the south coast of the southwesternmost point of Messenia lie the Messinian Oinousses islands. The largest of these are Sapientza, Schiza and Venetiko. The small island Sphacteria closes off the bay of Pylos. All these islands are virtually uninhabited.
Climate may vary, in the lowlands, temperatures are a bit warmer than Athens. Snow is not common during winter months except for the mountains, especially the Taygetus. Rain and clouds are common inland.
Before the 2010 reorganization, Messenia was a nomos (prefecture) containing 29 dimoi (municipalities) and 2 koinotites (communities). Since 2024, Messenia has been a perifereiake enoteta (regional unit) containing only 6 municipalities, but with the same population, as it did not change area in the reorganization. Some 25 municipalities and communities were incorporated politically into the other 6 according to the table below, becoming municipal units.
The prefecture of Messenia was previously subdivided into four provinces (επαρχίες, "eparchies") :
Province of Kalamon - Kalamata
Province of Messini - Messine
Province of Pylia - Pylos
Province of Tryphilia - Kyparissia
Like all provinces of Greece, they were abolished after the 2006 local elections, in line with Law 2539/1997, as part of the "Kapodistrias reform".