Barry Simon is the IBM Professor of Mathematics and Theoretical Physics at the California Institute of Technology. He is known for foundational contributions to spectral theory, functional analysis, and nonrelativistic quantum mechanics, especially Schrödinger operators and their applications to atomic and molecular physics. His work spans mathematical physics, including quantum field theory, statistical mechanics, Brownian motion, random matrix theory, multiparticle quantum systems, spectral and inverse spectral analysis, semiclassical limits, and orthogonal polynomials. Simon has also made influential contributions to the study of phase transitions, resonances, and random/ergodic Schrödinger operators, and is the author of widely used foundational texts in mathematical physics.