  The geometrical structures (in the sense of E. Cartan) are analyzed which
underlie the gravitational radiation phenomenon. Among the results are : - the
introduction of the adapted frame bundle to a congruence of isotropic
hypersurfaces in a Lorentzian manifold, - the description of the reduced frame
bundle which admits a unique radiation connection induced from the ambiant
space-time one, - the determination of the automorphisms of an integrable
radiation structure, - the repercussions of the geometry on the shape of the
stress-energy tensor in the Einstein's field equations.
