Messenia (; Messinia, ) is a regional unit (perifereiaki enotita) in the southwestern part of the Peloponnese, one of 13 regions into which Greece has been divided by the Kallikratis plan, implemented 1 January 2011. Before 2011 Messenia was a nomos (prefecture). The capital and the biggest city of Messenia in either case has been the city of Kalamata.