Barry Martin Simon (born 16 April 1946) is an American mathematical physicist and the IBM Professor of Mathematics and Theoretical Physics at Caltech,known for his prolific contributions in spectral theory, functional analysis, and nonrelativistic quantum mechanics (particularly Schrödinger operators), including the connections to atomic and molecular physics. He has authored more than 400 publications on mathematics and physics.He received Henri Poincaré Prize in 2012.