John Clarke Slater (December 22, 1900 – July 25, 1976) was a noted American physicist who made major contributions to the theory of the electronic structure of atoms, molecules and solids. He also made major contributions to microwave electronics. He received a B.S. in Physics from the University of Rochester in 1920 and a Ph.D. in Physics from Harvard in 1923, then did post-doctoral work at the universities of Cambridge (briefly) and Copenhagen. On his return to the U.S. he joined the Physics Department at Harvard.