Erik Christian Clemmensen (1876 - May 21, 1941) was a Danish-American chemist.
Clemmensen was born in Odense, Denmark. Clemmensen studied at Polytechnical University in Copenhagen. He emigrated to the United States in 1900 and worked in the pharmaceutical industry. For the invention of the Clemmensen reduction, he received his Ph.D. in 1913 from the University of Copenhagen.