  In General Relativity, the propagation of electromagnetic waves is usually
described by the vacuum Maxwell's equations on a fixed curved background. In
the limit of infinitely high frequencies, electromagnetic waves can be
localized as point particles, following null geodesics. However, at finite
frequencies, electromagnetic waves can no longer be treated as point particles
following null geodesics, and the spin angular momentum of light comes into
play, via the spin-curvature coupling. We will refer to this effect as the
gravitational spin Hall effect of light. Here, we review a series of
theoretical results related to the gravitational spin Hall effect of light, and
we compare the predictions of different models. The analogy with the spin Hall
effect in Optics is also explored, since in this field the effect is well
understood, both theoretically and experimentally.
