Messini is a municipal unit and the seat town of the municipality of Messini. It is located within the regional unit of Messenia in the Peloponnese region of Greece.
The administrative status of the area has evolved under various legislative frameworks. Prior to 2011, the hierarchy was governed by Law 2539 of 1997, known as the Kapodistrias Plan; during that period, Messenia was classified as a nomos and the municipal unit was designated as a locality.