Wilhelm Karl Klemm  (5 January 1896 – 24 October 1985) was an inorganic and physical chemist. 
Klemm did extensive work on intermetallic compounds, rare earth metals, transition elements and compounds involving oxygen and fluorine. 
He and Heinrich Bommer were the first to isolate elemental erbium (1934) and ytterbium (1936).
Klemm refined Eduard Zintl's ideas about the structure of intermetallic compounds and their connections to develop the Zintl-Klemm concept.
Klemm co-authored one of the ten most-cited papers in the history of the journal Zeitschrift für anorganische und allgemeine Chemie.
His textbooks on inorganic chemistry became standard works for chemists. His Magnetochemie (c1936) is considered foundational to magnetochemistry. Anorganische Chemie (Inorganic Chemistry) by Klemm and Rudolf Hoppe has been described as a legendary work by two titans of solid state chemistry.
Klemm was the second President of the Gesellschaft Deutscher Chemiker (GDCh), serving from 1952 to 1953. 
He was President of the International Union of Pure and Applied Chemistry (IUPAC) from 1965 to 1967.  Klemm co-edited the journal Zeitschrift für anorganische und allgemeine Chemie from 1939 to 1965. 
Since 1985, the GDCh has awarded the Wilhelm Klemm Prize in his honor.