Olli Ilmari Rehn ( pronunciation (help·info)) (born 31 March 1962) is a Finnish politician, currently serving as European Commissioner for Enlargement. Recently his name has come up as a potential presidential candidate for the 2012 election in Finland. In November 2009 he was nominated for the Economic and Monetary Affairs portfolio in the second Barroso Commission.

Born in Mikkeli in Eastern Finland, Rehn studied economics, international relations and journalism at Macalester College, Saint Paul, Minnesota, U.S.A.. He took a master's degree in political science from the University of Helsinki in 1989, and a PhD from the University of Oxford in 1996 on the subject of "Corporatism and Industrial Competitiveness in Small European States".

Rehn also played football for his hometown club Mikkelin Palloilijat in Finland's top division Mestaruussarja (now Veikkausliiga) in his youth.