  The authors study the geometry of lightlike hypersurfaces on manifolds $(M,
c)$ endowed with a pseudoconformal structure $c = CO (n - 1, 1)$ of Lorentzian
signature. Such hypersurfaces are of interest in general relativity since they
can be models of different types of physical horizons. On a lightlike
hypersurface, the authors consider the fibration of isotropic geodesics and
investigate their singular points and singular submanifolds. They construct a
conformally invariant normalization of a lightlike hypersurface intrinsically
connected with its geometry and investigate affine connections induced by this
normalization. The authors also consider special classes of lightlike
hypersurfaces. In particular, they investigate lightlike hypersurfaces for
which the elements of the constructed normalization are integrable.
