The Martinikerk (Martin's church) is the oldest church in Groningen, The Netherlands. The church and its associated tower (the Martinitoren) are named after Saint Martin of Tours (316–397), the patron saint of the Archbishopric of Utrecht to which Groningen belongs.
The church has been a cathedral for a short period during the first bishopric of Groningen (1559–1594).
The origins of the Martinikerk are a cruciform church built in the 13th century, which was extended in the 15th and 16th centuries.
The tower was built from 1469 till 1482, with later additions. Citizens of Groningen often refer to the tower as d'Olle Grieze (Old Grey One). The original 13th century tower was destroyed by lightning and a new tower was built in the 15th century, also destroyed by lightning.