A b s t r ac t . Let G be a finite group acting linearly on a vector space V . We consider the linear symmetry groups GL(Gv) of orbits Gv ⊆ V , where the linear symmetry group GL(S) of a subset S ⊆ V is defined as the set of all linear maps of the linear span of S which permute S. We assume that V is the linear span of at least one orbit Gv. We define a set of generic points in V , which is Zariskiopen in V , and show that the groups GL(Gv) for v generic are all isomorphic, and isomorphic to a subgroup of every symmetry group GL(Gw) such that V is the linear span of Gw. If the underlying characteristic is zero, "isomorphic" can be replaced by "conjugate in GL(V )". Moreover, in the characteristic zero case, we show how the character of G on V determines this generic symmetry group. We apply our theory to classify all affine symmetry groups of vertex-transitive polytopes, thereby answering a question of Babai (1977).2010 Mathematics Subject Classification. Primary 52B15, Secondary 05E15, 20B25, 20C15.