Marius Job Cohen (Haarlem, October 18, 1947) is a Dutch former politician and administrator. From 2014 to 2018, Cohen was a professor of municipal law and municipal studies at Leiden University; he held the so-called Thorbecke Chair. Cohen was Mayor of Amsterdam from January 15, 2001, to March 12, 2010. He was Political Leader of the Labour Party from April 25, 2010, to February 20, 2012. He was a member of the House of Representatives from June 10, 2010, to February 28, 2012, and PvdA parliamentary group leader until February 20, 2012.