Ketzin (, <small>official name:</small> Ketzin/Havel) is a town in the Havelland district, in Brandenburg, Germany. It is situated on the river Havel, 17 km northwest of Potsdam, and 40 km west of Berlin.
Ketzin was first mentioned in 1197 by a document. Until 1571, Ketzin was kept in the Bishopric of Brandenburg, the imperial principality of the Prince-bishop of the Diocese of Brandenburg and according to the law, not part of the Margraviate of Brandenburg.
The town counts 6 Ortsteile (civil parishes): Etzin, Falkenrehde, Knoblauch, Paretz, Tremmen and Zachow.
The Ketzin Cable Ferry, a vehicular cable ferry, crosses the Havel between Ketzin and Schmergow.