Ján Veizer (born 22 June 1941) is the Distinguished University Professor (emeritus) of Earth Sciences at the University of Ottawa and Institute for Geology, Mineralogy und Geophysics, of Bochum Ruhr University. He held the NSERC/Noranda/CIFAR Industrial Chair in Earth System Isotope and Environmental Geochemistry until 2004. He is an isotope geochemist; his research interests have included the use of chemical and isotopic techniques in determining Earth's climatic and environmental history.