Messini () is a municipal unit (dimotiki enotita) and seat (edra) of the municipality (dimos) of Messini within the regional unit (perifereiaki enotita) of Messenia in the region (perifereia) of Peloponnese, one of 13 regions into which Greece has been divided. Before 2011 the same hierarchy prevailed, according to Law 2539 of 1997, the Kapodistrias Plan, except that Messenia was a nomos and the Municipal unit was a locality (topiko diamerisma).