William Michael Gelbart (born June 12, 1946) is Distinguished Professor of Chemistry and Biochemistry at the University of California, Los Angeles, and a member of the California NanoSystems Institute and the UCLA Molecular Biology Institute. He obtained his Bachelor of Science degree from Harvard University in 1967, his Master's (1968) and PhD (1970) degrees from the University of Chicago, and did postdoctoral work at the University of Paris (1971) and the University of California, Berkeley (1972). After 30 years of research in theoretical physical chemistry, contributing notably to the fields of  gas-phase photophysics, optical properties of simple liquids, and the statistical physics of complex fluids, he started a biophysics laboratory with Charles Knobler in 2002 to investigate the physical aspects of viral infectivity.