Oppido Mamertina (Calabrian Greek: Oppidù, Ofidus) is a town and comune of the province of Reggio Calabria in Calabria in southern Italy at about 62 kilometres (39 mi) northeast of Reggio Calabria and about 120 kilometres (75 mi) southwest of Catanzaro.

It is the seat of the Diocese of Oppido Mamertina.

The municipality includes the following boroughs (frazioni): Castellace, Messignadi, Piminoro, and Tresilico.

The Taurani, Oscan-speaking Italic people from Bruttii, built a large town at the site of Mella near the present Oppido Vecchio in the 4th c. BC after taking over peacefully from Greek Locri, some 15 miles away. who had controlled the area.

The Greek influence in the town is shown by the street plan, building styles and many Greek coins. Later after supporting Hannibal in the 2nd Punic War (218–201 BC), the Tauriani returned to the protection of the Romans who later expanded the town.

The first mention of the town (Oppidum in Latin, meaning citadel) is 1040, during the Byzantine Era.

The town is famous for its prolonged resistance before falling to Roger the Norman in 1056.

On February 5, 1783, an earthquake completely destroyed the town killing 1,198 people. The town was rebuilt near the neighbouring village Tresilico (incorporated in the municipality in 1927). Other earthquakes hit the town in 1894 and on December 28, 1908, which destroyed the neighbouring township Castellace.

The economy is based on agriculture, in particular olive groves and the production of olive oil, as well citrus orchards in the plain. Forestry and sheep husbandry are also sources of income.

The town is home to the 'Ndrangheta, a Mafia-type criminal organization based in Calabria. Several powerful criminal clans originate from the town, such as the Mammoliti-Rugolo.

The town achieved a sad notoriety in July 2014 when, two weeks after Pope Francis, visiting Calabria, had publicly excommunicated the Mafia, a procession carrying a statue of the Madonna stopped to pay homage outside the house of a home confined local mafia leader.

The population halved during the last century. Many inhabitants moved to the industrial centres in northern Italy or joined the Italian diaspora to escape the extreme poverty.

• Salvatore Albano (1841-1893), sculptor
• Rocky Gattellari (1941-2023), boxer, Olympian, political candidate and businessman
• Saverio Mammoliti (born 1942), 'Ndrangheta boss
• Alessio Viola (born 1990), footballer

 This article incorporates text from a publication now in the public domain: Herbermann, Charles, ed. (1913). "Oppido Mamertina". Catholic Encyclopedia. New York: Robert Appleton Company.