Robert Miller Hardt (born 24 June 1945, Pittsburgh)^[1] is an American mathematician. His research deals with geometric measure theory, partial differential equations, and continuum mechanics. He is particularly known for his work with Leon Simon proving the boundary regularity of volume minimizing hypersurfaces.

Hardt received in 1967 his bachelor's degree from Massachusetts Institute of Technology and in 1971 his Ph.D. from Brown University under Herbert Federer with thesis Slicing and Intersection Theory for Chains Associated with Real Analytic Varieties.^[2] In 1971 he became an instructor and later a professor at the University of Minnesota. In 1988 he became a professor at Rice University, where he is W. L. Moody Professor. His doctoral students include Fang-Hua Lin.

Hardt was a visiting scholar at the Institute for Advanced Study in 1976 and at IHES in 1978 and 1981. He was a visiting professor at the University of Melbourne in 1979, at Stanford University and at the University of Wuppertal.

In 1986 Hardt was an Invited Speaker at the ICM in Berkeley, California. In 2015 he was elected a Fellow of the American Mathematical Society.