Robinson manifolds and the shear-free condition

This paper is a short summary of the talk on Robinson manifolds and Cauchy-Riemann spaces given at Journees Relativistes 2001 in Dublin. It recalls two generalizations of the definition of shear-free congruences of null geodesics. These generalizations are equivalent in dimension 4, but not in higher dimensions, as illustrated on an example described by Ivor Robinson during that conference.