Stephen M. Barr is a professor in the Department of Physics and Astronomy of the University of Delaware. His physics research interests include theoretical particle physics. His particular areas of expertise are grand unified theories, theories of CP violation, theories of neutrino masses and mixing, and particle cosmology, especially theories of baryogenesis and dark matter.

He was elected a Fellow of the American Physical Society in 2011 "for original contributions to grand unified theories, CP violation, and baryogenesis".

Dr. Barr has also written and lectured extensively on the relation of science and religion. He is a believing and practicing Catholic, and was elected to the Academy of Catholic Theology in 2010. He is a member of the editorial Advisory Council of First Things magazine.