William Summer Johnson (February 24, 1913 – August 19, 1995) was an American chemist and teacher. From 1940 to 1958, Dr. Johnson was an instructor and then professor at the University of Wisconsin–Madison. In 1958, he moved to Stanford University in California where he spent the remainder of his scientific career. He did important research in the artificial production of steroids and was awarded the National Medal of Science in 1987. The Lemieux–Johnson oxidation, in which an olefin is converted into two aldehyde or ketone fragments, is named after him and Raymond Lemieux.