  We give a short review of the spin foam models of quantum gravity, with an
emphasis on the Barret-Crane model. After explaining the shortcomings of the
Barret-Crane model, we briefly discuss two new approaches, one based on the 3d
spin foam state sum invariants for the embedded spin networks, and the other
based on representing the string scattering amplitudes as 2d spin foam state
sum invariants.
