John Joseph Hopfield (born Jan Józef Chmielewski; July 8, 1891 – January 8, 1953) was a Polish-American physicist.
For about a decade he was an industrial physicist working with technologies for fabricating glass windows, and was the inventor listed on several related patents.
At Syracuse, he had worked as an assistant with Raymond Thayer Birge, who moved to University of California, Berkeley around this time.
He became an instructor and assistant professor of physics at Berkeley, and was awarded a Guggenheim Fellowship in 1928 to work with Friedrich Paschen for a year in Berlin.
With the onset of the Second World War, physicists were again in great demand, and he moved to Washington, D.C., to participate in war-related research.