Sybren Ruurds de Groot (born 18.04.1916) is a Dutch theoretical physicist and a member of the Royal Netherlands Academy of Arts and Sciences (1958). He was born in Amsterdam. In 1945 he received the degree of Doctor of Philosophy at the University of Amsterdam. In 1948 — 53 he was professor at the university in Utrecht, in 1953 — 64 at the University of Leiden and from 1964 at the University of Amsterdam.
His work is in the field of statistical mechanics and the thermodynamics of irreversible processes, nuclear physics, relativistic physics and electrodynamics. He is one of the founders of modern non-equilibrium thermodynamics. He studied effects in the case of allowed beta transitions and calculated the distribution of the directions of the radiation from groups of nuclei in the absence of rotational symmetry.