The Martinitoren (Martini Tower) is the highest church tower in the city of Groningen , The Netherlands. The tower is located at the north-western corner of the Grote Markt (Main Square), is part of the Martinikerk (Martini Church). The carillon within the tower contains 62 bells. The citizens of Groningen call their tower d'Olle Grieze, meaning the old grey one in the local dialect. It is considered one of the main tourist attractions of Groningen and offers a great view over the city and surrounding area. The front of the tower shows three pictures above the entrance: the blind man Bernlef, Saint Martinus and Rudolf Agricola. All three are men who are linked to the history of Groningen. According to reports the tower has a foundation only three meters deep.

Twice before a tower has stood on the site of the current Martinitoren. The first was built in the 13th century; this was approximately 30 meters high and built in the Romanesque style. This tower was destroyed by a lightning bolt. In the 15th century a second tower was built, approximately 45 meters high, but it also was devastated by a lightning storm. The third and current tower was largely built between 1469 and 1482 from blocks of Bentheimer sandstone. The steeple wasn't finished until the mid-16th century. This tower was initially an estimated 102 meters high. Its architecture was influenced by the Dom Tower of Utrecht. The lighting of celebratory fires on the third gallery, after the departure of Spanish and Walloon troops in 1577, caused the tower to partially collapse. However, the remaining portion kept a height of 69 meters. In the 17th century the tower was repaired up to the current 97 meter height. Later the tower was damaged several times by natural violence and several wars. In the bells, a bullet hole can still be found, as result of severe fighting when the Canadian Forces liberated Groningen at the end of World War II.