Wouter Koolmees (born 20 March 1977) is a Dutch economist, politician and business executive of the Democrats 66 (D66) party. He served as Minister of Social Affairs and Employment in the Third Rutte cabinet from 2017 to 2022, and briefly as acting Deputy Prime Minister of the Netherlands in 2019–2020. Since 1 November 2022, he has served as President and CEO of Nederlandse Spoorwegen (NS), the principal Dutch national railway operator.